diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/HtmlReportEngine.cs b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/HtmlReportEngine.cs
index a16e0dad4f..6b3471f7ba 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/HtmlReportEngine.cs
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/HtmlReportEngine.cs
@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using Microsoft.Testing.Extensions.HtmlReport.Resources;
+using Microsoft.Testing.Platform;
 using Microsoft.Testing.Platform.CommandLine;
 using Microsoft.Testing.Platform.Configurations;
 using Microsoft.Testing.Platform.Extensions.TestFramework;
@@ -64,11 +65,19 @@ public HtmlReportEngine(
             out string[]? providedFileName);
 
         string fileName = fileNameExplicitlyProvided
-            ? providedFileName![0]
+            ? ResolveHtmlFileName(GetProvidedFileName(providedFileName))
             : BuildDefaultFileName(finishTime);
 
         string outputDirectory = _configuration.GetTestResultDirectory();
+        // Path.Combine short-circuits when the second argument is rooted, so an absolute
+        // user-provided file name overrides the test results directory while validated
+        // relative paths stay nested under it.
         string finalPath = Path.Combine(outputDirectory, fileName);
+        string? finalDirectory = Path.GetDirectoryName(finalPath);
+        if (!RoslynString.IsNullOrEmpty(finalDirectory))
+        {
+            _fileSystem.CreateDirectory(finalDirectory);
+        }
 
         string template = LoadTemplate();
         string json = BuildJson(results, finishTime);
@@ -82,6 +91,11 @@ public HtmlReportEngine(
         return await WriteWithRetryAsync(finalPath, bytes, fileNameExplicitlyProvided).ConfigureAwait(false);
     }
 
+    private static string GetProvidedFileName(string[]? providedFileName)
+        => providedFileName is { Length: > 0 }
+            ? providedFileName[0]
+            : throw ApplicationStateGuard.Unreachable();
+
     private async Task<(string FileName, string? Warning)> WriteWithRetryAsync(string finalPath, byte[] bytes, bool fileNameExplicitlyProvided)
     {
         // Explicit file names: use FileMode.Create (overwrite). Default-generated file
@@ -154,6 +168,19 @@ private string BuildDefaultFileName(DateTimeOffset finishTime)
         return ReplaceInvalidFileNameChars(raw);
     }
 
+    private string ResolveHtmlFileName(string template)
+    {
+        string processName = Path.GetFileNameWithoutExtension(_testApplicationModuleInfo.GetCurrentTestApplicationFullPath());
+        string processId = _environment.ProcessId.ToString(CultureInfo.InvariantCulture);
+        Dictionary<string, string> replacements = ArtifactNamingHelper.GetStandardReplacements(processName, processId, _clock.UtcNow);
+        string resolved = ArtifactNamingHelper.ResolveTemplate(template, replacements);
+        string directoryPart = Path.GetDirectoryName(resolved) ?? string.Empty;
+        string sanitizedFileName = ReplaceInvalidFileNameChars(Path.GetFileName(resolved));
+        return directoryPart.Length == 0
+            ? sanitizedFileName
+            : Path.Combine(directoryPart, sanitizedFileName);
+    }
+
     private static string GetTargetFrameworkMoniker()
         => TargetFrameworkParser.GetShortTargetFramework(
             Assembly.GetEntryAssembly()?.GetCustomAttribute<TargetFrameworkAttribute>()?.FrameworkDisplayName)
@@ -163,13 +190,46 @@ private static string GetTargetFrameworkMoniker()
     private static string ReplaceInvalidFileNameChars(string fileName)
     {
         var sb = new StringBuilder(fileName.Length);
-        char[] invalid = Path.GetInvalidFileNameChars();
         foreach (char c in fileName)
         {
-            sb.Append(Array.IndexOf(invalid, c) >= 0 ? '_' : c);
+            sb.Append(IsInvalidFileNameChar(c) ? '_' : c);
         }
 
-        return sb.ToString();
+        string replaced = sb.ToString().TrimEnd();
+        if (IsReservedFileName(replaced))
+        {
+            replaced = '_' + replaced;
+        }
+
+        return replaced;
+    }
+
+    private static bool IsInvalidFileNameChar(char c)
+        // Keep the explicit file-name sanitization aligned with TRX report naming so
+        // placeholders and cross-platform reserved characters produce compatible names.
+        => c is < ' ' or '"' or '<' or '>' or '|' or ':' or '*' or '?' or '\\' or '/' or '@' or '(' or ')' or '^' or ' ';
+
+    private static bool IsReservedFileName(string fileName)
+    {
+        string bareName = fileName;
+        int dot = bareName.IndexOf('.');
+        if (dot >= 0)
+        {
+            bareName = bareName.Substring(0, dot);
+        }
+
+        return bareName.Equals("CON", StringComparison.OrdinalIgnoreCase)
+            || bareName.Equals("PRN", StringComparison.OrdinalIgnoreCase)
+            || bareName.Equals("AUX", StringComparison.OrdinalIgnoreCase)
+            || bareName.Equals("NUL", StringComparison.OrdinalIgnoreCase)
+            || bareName.Equals("CLOCK$", StringComparison.OrdinalIgnoreCase)
+            || IsReservedNameWithNumber(bareName, "COM")
+            || IsReservedNameWithNumber(bareName, "LPT");
+
+        static bool IsReservedNameWithNumber(string bareName, string prefix)
+            => bareName.Length == 4
+                && bareName.StartsWith(prefix, StringComparison.OrdinalIgnoreCase)
+                && bareName[3] is >= '1' and <= '9';
     }
 
     private static string LoadTemplate()
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/HtmlReportGeneratorCommandLine.cs b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/HtmlReportGeneratorCommandLine.cs
index 5c798c1101..3635b156ee 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/HtmlReportGeneratorCommandLine.cs
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/HtmlReportGeneratorCommandLine.cs
@@ -14,6 +14,8 @@ internal sealed class HtmlReportGeneratorCommandLine : ICommandLineOptionsProvid
     public const string HtmlReportOptionName = "report-html";
     public const string HtmlReportFileNameOptionName = "report-html-filename";
 
+    private static readonly char[] DirectorySeparators = [Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar];
+
     /// <inheritdoc />
     public string Uid => nameof(HtmlReportGeneratorCommandLine);
 
@@ -40,19 +42,28 @@ public Task<ValidationResult> ValidateOptionArgumentsAsync(CommandLineOption com
     {
         if (commandOption.Name == HtmlReportFileNameOptionName)
         {
-            string fileName = arguments[0];
+            if (arguments.Length is 0)
+            {
+                return ValidationResult.InvalidTask(ExtensionResources.HtmlReportFileNameMustNotBeEmpty);
+            }
 
-            // Validate "pure file name" first. We don't want any path component, drive letter,
-            // parent directory traversal, leading/trailing whitespace or invalid file name char.
-            if (!IsValidPureFileName(fileName))
+            string argument = arguments[0];
+
+            string fileNamePart = Path.GetFileName(argument);
+            if (RoslynString.IsNullOrWhiteSpace(fileNamePart))
             {
-                return ValidationResult.InvalidTask(ExtensionResources.HtmlReportFileNameShouldNotContainPath);
+                return ValidationResult.InvalidTask(ExtensionResources.HtmlReportFileNameMustNotBeEmpty);
             }
 
-            if (!fileName.EndsWith(".html", StringComparison.OrdinalIgnoreCase))
+            if (!fileNamePart.EndsWith(".html", StringComparison.OrdinalIgnoreCase))
             {
                 return ValidationResult.InvalidTask(ExtensionResources.HtmlReportFileNameExtensionIsNotHtml);
             }
+
+            if (EscapesResultsDirectory(argument))
+            {
+                return ValidationResult.InvalidTask(ExtensionResources.HtmlReportFileNameRelativePathMustStayUnderResultsDirectory);
+            }
         }
 
         return ValidationResult.ValidTask;
@@ -65,75 +76,64 @@ public Task<ValidationResult> ValidateCommandLineOptionsAsync(ICommandLineOption
                 ? ValidationResult.InvalidTask(ExtensionResources.HtmlReportIsNotValidForDiscovery)
                 : ValidationResult.ValidTask;
 
-    // We are intentionally strict here so that we cannot be tricked across platforms.
-    // The argument must be a "pure" file name: no directory separator, no drive letter,
-    // no parent directory traversal, no invalid file name character, no leading/trailing
-    // whitespace, no Windows reserved device name. We use a hard-coded list of invalid
-    // characters (a superset of Path.GetInvalidFileNameChars() on Linux + Windows) so
-    // the same input is rejected regardless of the host OS.
-    private static readonly char[] InvalidFileNameChars =
-    [
-        '\0', '/', '\\', ':', '*', '?', '"', '<', '>', '|',
-        '\u0001', '\u0002', '\u0003', '\u0004', '\u0005', '\u0006', '\u0007',
-        '\b', '\t', '\n', '\u000b', '\u000c', '\r',
-        '\u000e', '\u000f', '\u0010', '\u0011', '\u0012', '\u0013', '\u0014',
-        '\u0015', '\u0016', '\u0017', '\u0018', '\u0019', '\u001a', '\u001b',
-        '\u001c', '\u001d', '\u001e', '\u001f',
-    ];
-
-    // Windows reserved device names. CreateFile on Windows will redirect a file
-    // named e.g. CON.html to the actual device. Rejecting them up-front means the
-    // option doesn't pass validation but then explode later in WriteAsync.
-    private static readonly string[] WindowsReservedNames =
-    [
-        "CON", "PRN", "AUX", "NUL",
-        "COM0", "COM1", "COM2", "COM3", "COM4", "COM5", "COM6", "COM7", "COM8", "COM9",
-        "LPT0", "LPT1", "LPT2", "LPT3", "LPT4", "LPT5", "LPT6", "LPT7", "LPT8", "LPT9",
-    ];
-
-    private static bool IsValidPureFileName(string fileName)
+    private static bool EscapesResultsDirectory(string path)
     {
-        if (RoslynString.IsNullOrWhiteSpace(fileName))
+        // Fully-qualified paths (e.g. "C:\foo.html", "\\server\share\foo.html" or "/foo.html") are
+        // accepted as-is and validated by the OS when we open the file - the user explicitly opted
+        // out of writing under the test results directory.
+        if (IsPathFullyQualified(path))
         {
             return false;
         }
 
-        if (fileName != fileName.Trim())
+        // Drive-relative paths on Windows such as "C:foo.html" are "rooted" but not fully qualified -
+        // they resolve against the current directory of the drive, which is unpredictable and would
+        // silently escape the test results directory. Reject them. On non-Windows OSes
+        // Path.IsPathRooted only returns true for paths starting with "/", which are already handled
+        // above, so this check is effectively Windows-only and matches the TRX option behavior.
+        if (Path.IsPathRooted(path))
         {
-            return false;
+            return true;
         }
 
-        if (fileName == "." || fileName == ".." || fileName.Contains(".."))
+        // Any remaining ".." segment in a relative path would escape the test results directory.
+        return path.Split(DirectorySeparators, StringSplitOptions.RemoveEmptyEntries).Any(segment => segment == "..");
+    }
+
+    private static bool IsPathFullyQualified(string path)
+    {
+#if NETCOREAPP
+        return Path.IsPathFullyQualified(path);
+#else
+        // Mirrors the runtime implementation that is missing on .NET Framework and netstandard2.0.
+        if (path.Length < 2)
         {
             return false;
         }
 
-        foreach (char c in fileName)
+        // UNC paths like "\\server\share" (or with forward slashes).
+        if (IsDirectorySeparator(path[0]) && IsDirectorySeparator(path[1]))
         {
-            if (Array.IndexOf(InvalidFileNameChars, c) >= 0)
-            {
-                return false;
-            }
+            return true;
         }
 
-        // Disallow Windows device names independent of host OS so the option is
-        // consistently rejected. We compare against the bare name (without extension)
-        // because e.g. "CON.html" maps to the CON device.
-        string bareName = fileName;
-        int dot = bareName.IndexOf('.');
-        if (dot >= 0)
+        // On Unix, only paths starting with "/" are fully qualified.
+        if (Path.DirectorySeparatorChar == '/')
         {
-            bareName = bareName.Substring(0, dot);
+            return path[0] == '/';
         }
 
-        foreach (string reserved in WindowsReservedNames)
-        {
-            if (string.Equals(bareName, reserved, StringComparison.OrdinalIgnoreCase))
-            {
-                return false;
-            }
-        }
+        // On Windows, fully qualified drive paths must be "X:\" or "X:/".
+        return path.Length >= 3
+            && IsValidDriveLetter(path[0])
+            && path[1] == ':'
+            && IsDirectorySeparator(path[2]);
+
+        static bool IsDirectorySeparator(char c)
+            => c == Path.DirectorySeparatorChar || c == Path.AltDirectorySeparatorChar;
 
-        return true;
+        static bool IsValidDriveLetter(char c)
+            => c is (>= 'A' and <= 'Z') or (>= 'a' and <= 'z');
+#endif
     }
 }
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Microsoft.Testing.Extensions.HtmlReport.csproj b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Microsoft.Testing.Extensions.HtmlReport.csproj
index 83a09753a0..f3d2d5f0da 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Microsoft.Testing.Extensions.HtmlReport.csproj
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Microsoft.Testing.Extensions.HtmlReport.csproj
@@ -44,6 +44,7 @@ This package extends Microsoft Testing Platform to produce self-contained HTML t
     <Compile Include="$(RepoRoot)src\Platform\Microsoft.Testing.Platform\Helpers\RoslynString.cs" Link="Helpers\RoslynString.cs" />
     <Compile Include="$(RepoRoot)src\Platform\Microsoft.Testing.Platform\Helpers\ApplicationStateGuard.cs" Link="Helpers\ApplicationStateGuard.cs" />
     <Compile Include="$(RepoRoot)src\Platform\Microsoft.Testing.Platform\Helpers\ExitCodes.cs" Link="Helpers\ExitCodes.cs" />
+    <Compile Include="$(RepoRoot)src\Platform\Microsoft.Testing.Platform\Services\ArtifactNamingHelper.cs" Link="Services\ArtifactNamingHelper.cs" />
     <Compile Include="$(RepoRoot)src\Platform\Microsoft.Testing.Platform\OutputDevice\TargetFrameworkParser.cs" Link="Helpers\TargetFrameworkParser.cs" />
     <Compile Include="$(RepoRoot)src\Platform\Microsoft.Testing.Platform\Resources\PlatformResources.cs" Link="Resources\PlatformResources.cs" />
   </ItemGroup>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/ExtensionResources.resx b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/ExtensionResources.resx
index 3e5d997cf1..c00a8d5937 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/ExtensionResources.resx
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/ExtensionResources.resx
@@ -70,15 +70,20 @@
   <data name="HtmlReportFileNameExtensionIsNotHtml" xml:space="preserve">
     <value>'--report-html-filename' file name argument must end with '.html' (e.g. --report-html-filename myreport.html)</value>
   </data>
+  <data name="HtmlReportFileNameMustNotBeEmpty" xml:space="preserve">
+    <value>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</value>
+  </data>
   <data name="HtmlReportFileNameOptionDescription" xml:space="preserve">
-    <value>The name of the generated HTML report</value>
+    <value>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</value>
+  </data>
+  <data name="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory" xml:space="preserve">
+    <value>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</value>
   </data>
   <data name="HtmlReportFileNameRequiresHtmlReport" xml:space="preserve">
     <value>'--report-html-filename' requires '--report-html' to be enabled</value>
   </data>
-  <data name="HtmlReportFileNameShouldNotContainPath" xml:space="preserve">
-    <value>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</value>
-  </data>
   <data name="HtmlReportGeneratorDescription" xml:space="preserve">
     <value>Produce a self-contained HTML report for the current test session</value>
   </data>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.cs.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.cs.xlf
index db2ff9b5fc..a17c5265e5 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.cs.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.cs.xlf
@@ -22,9 +22,21 @@
         <target state="translated">Argument názvu souboru „--report-html-filename“ musí končit na .html (např. --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">Název vygenerované sestavy HTML</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">Název vygenerované sestavy HTML</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">„--report-html-filename“ vyžaduje povolení „--report-html“</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">Argument názvu souboru nesmí obsahovat cestu nebo neplatné znaky (např. --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">Vytvoření samostatné sestavy HTML pro aktuální testovací relaci</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.de.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.de.xlf
index fe2c7404f8..432d8694fc 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.de.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.de.xlf
@@ -22,9 +22,21 @@
         <target state="translated">Das Dateinamenargument „--report-html-filename“ muss mit „.html“ enden (z. B. --report-html-filename myreport.html).</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">Der Name des generierten HTML-Berichts.</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">Der Name des generierten HTML-Berichts.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">„--report-html-filename“ erfordert, dass „--report-html“ aktiviert ist.</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">Das Dateinamenargument darf keinen Pfad und keine ungültigen Zeichen enthalten (z. B. --report-html-filename myreport.html).</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">Erstellt einen eigenständigen HTML-Bericht für die aktuelle Testsitzung</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.es.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.es.xlf
index 75b6592d33..0246dbc161 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.es.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.es.xlf
@@ -22,9 +22,21 @@
         <target state="translated">El argumento del nombre de archivo '--report-html-filename' debe terminar en '.html' (por ejemplo, --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">Nombre del informe HTML generado</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">Nombre del informe HTML generado</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">'--report-html-filename' requiere que '--report-html' esté habilitado</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">el argumento de nombre de archivo no debe contener una ruta de acceso ni caracteres no válidos (por ejemplo, --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">Generar un informe HTML independiente para la sesión de prueba actual</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.fr.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.fr.xlf
index 3b28815b6e..da6612001d 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.fr.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.fr.xlf
@@ -22,9 +22,21 @@
         <target state="translated">L’argument de nom de fichier de « --report-html-filename » doit se terminer par « .html » (par exemple, --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">Nom du rapport HTML généré</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">Nom du rapport HTML généré</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">« --report-html-filename » nécessite l’activation de « --report-html »</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">L’argument de nom de fichier ne doit pas contenir de chemin d’accès ni de caractères non valides (par exemple, --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">Générer un rapport HTML autonome pour la session de test actuelle</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.it.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.it.xlf
index 8d2ec09e31..a52ef541ea 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.it.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.it.xlf
@@ -22,9 +22,21 @@
         <target state="translated">L'argomento del nome file "--report-html-filename" deve terminare con ".html" (ad esempio --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">Nome del report HTML generato</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">Nome del report HTML generato</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">"--report-html-filename" richiede che "--report-html" sia abilitato</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">l'argomento del nome file non deve contenere un percorso o caratteri non validi (ad esempio --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">Generare un report HTML autonomo per la sessione di test corrente</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ja.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ja.xlf
index 97338ab96a..7f2a4136e7 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ja.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ja.xlf
@@ -22,9 +22,21 @@
         <target state="translated">'--report-html-filename' のファイル名引数の末尾は '.html' にする必要があります (例: --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">生成された HTML レポートの名前</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">生成された HTML レポートの名前</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">'--report-html-filename' を使用するには、'--report-html' を有効にする必要があります</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">ファイル名引数にパスや無効な文字を含めることはできません (例: --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">現在のテスト セッションの自己完結型 HTML レポートを生成する</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ko.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ko.xlf
index 38ad8285c6..497d49067e 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ko.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ko.xlf
@@ -22,9 +22,21 @@
         <target state="translated">'--report-html-filename' 파일 이름 인수는 '.html'로 끝나야 합니다. 예: --report-html-filename myreport.html</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">생성된 HTML 보고서의 이름</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">생성된 HTML 보고서의 이름</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">'--report-html-filename'을 사용하려면 '--report-html'을 사용하도록 설정해야 합니다.</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">파일 이름 인수에는 경로나 잘못된 문자가 포함되면 안 됩니다. 예: --report-html-filename myreport.html</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">현재 테스트 세션에 대한 독립 실행형 HTML 보고서 생성</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.pl.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.pl.xlf
index 7514281a8e..f7ff23bceb 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.pl.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.pl.xlf
@@ -22,9 +22,21 @@
         <target state="translated">Argument nazwy pliku „--report-html-filename” musi kończyć się ciągiem „.html” (np. --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">Nazwa wygenerowanego raportu HTML</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">Nazwa wygenerowanego raportu HTML</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">Element „--report-html-filename” wymaga włączenia parametru „--report-html”</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">argument nazwy pliku nie może zawierać ścieżki ani nieprawidłowych znaków (np. --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">Tworzenie samodzielnego raportu HTML dla bieżącej sesji testowej</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.pt-BR.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.pt-BR.xlf
index 4f8d2b4c8f..0034bb5adb 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.pt-BR.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.pt-BR.xlf
@@ -22,9 +22,21 @@
         <target state="translated">O argumento de nome de arquivo "--report-html-filename" deve terminar com ".html" (por exemplo, --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">O nome do relatório HTML gerado</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">O nome do relatório HTML gerado</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">"--report-html-filename" requer que "--report-html" esteja habilitado</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">o argumento de nome de arquivo não deve conter um caminho ou caracteres inválidos (por exemplo, --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">Produzir um relatório HTML autossuficiente para a sessão de teste atual</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ru.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ru.xlf
index 42a1d588ed..456b2115d8 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ru.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.ru.xlf
@@ -22,9 +22,21 @@
         <target state="translated">Аргумент имени файла "--report-html-filename" должен оканчиваться на ".html" (например: --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">Имя сгенерированного отчета в формате HTML</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">Имя сгенерированного отчета в формате HTML</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">Для "--report-html-filename" требуется включить "--report-html"</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">аргумент с именем файла не должен содержать путь или недопустимые символы (например: --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">Создать автономный отчет в формате HTML для текущего тестового сеанса</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.tr.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.tr.xlf
index f6271ce7d2..dae3cea660 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.tr.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.tr.xlf
@@ -22,9 +22,21 @@
         <target state="translated">'--report-html-filename' dosya adı bağımsız değişkeni '.html' ile bitmelidir (ör. --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">Oluşturulan HTML raporunun adı</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">Oluşturulan HTML raporunun adı</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">'--report-html-filename', '--report-html' seçeneğinin etkinleştirilmesini gerektirir</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">Dosya adı bağımsız değişkeni yol veya geçersiz karakterler içermemelidir (ör. --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">Geçerli test oturumu için bağımsız bir HTML raporu oluşturun</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.zh-Hans.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.zh-Hans.xlf
index 1d7e4bbf9f..9b52b1ac9b 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.zh-Hans.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.zh-Hans.xlf
@@ -22,9 +22,21 @@
         <target state="translated">"--report-html-filename" 文件名参数必须以 ".html" 结尾(例如 --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">生成的 HTML 报表的名称</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">生成的 HTML 报表的名称</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">"--report-html-filename" 需要启用 "--report-html"</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">文件名参数不得包含路径或无效字符(例如 --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">为当前测试会话生成独立的 HTML 报表</target>
diff --git a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.zh-Hant.xlf b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.zh-Hant.xlf
index 1401b444dc..8d0ba6c172 100644
--- a/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.zh-Hant.xlf
+++ b/src/Platform/Microsoft.Testing.Extensions.HtmlReport/Resources/xlf/ExtensionResources.zh-Hant.xlf
@@ -22,9 +22,21 @@
         <target state="translated">'--report-html-filename' 檔名引數的結尾必須是 '.html' (例如 --report-html-filename myreport.html)</target>
         <note />
       </trans-unit>
+      <trans-unit id="HtmlReportFileNameMustNotBeEmpty">
+        <source>'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</source>
+        <target state="new">'--report-html-filename' file name part must not be empty (e.g. --report-html-filename myreport.html)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="HtmlReportFileNameOptionDescription">
-        <source>The name of the generated HTML report</source>
-        <target state="translated">產生的 TRX 報告名稱</target>
+        <source>The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+Example: MyReport_{tfm}.html</source>
+        <target state="needs-review-translation">產生的 HTML 報告名稱</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="HtmlReportFileNameRelativePathMustStayUnderResultsDirectory">
+        <source>'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</source>
+        <target state="new">'--report-html-filename' relative paths must stay under the test results directory (e.g. --report-html-filename nested/myreport.html)</target>
         <note />
       </trans-unit>
       <trans-unit id="HtmlReportFileNameRequiresHtmlReport">
@@ -32,11 +44,6 @@
         <target state="translated">'--report-html-filename' 需要啟用 '--report-html'</target>
         <note />
       </trans-unit>
-      <trans-unit id="HtmlReportFileNameShouldNotContainPath">
-        <source>file name argument must not contain a path or invalid characters (e.g. --report-html-filename myreport.html)</source>
-        <target state="translated">檔案名稱引數不能包含路徑或無效字元 (例如 --report-html-filename myreport.html)</target>
-        <note />
-      </trans-unit>
       <trans-unit id="HtmlReportGeneratorDescription">
         <source>Produce a self-contained HTML report for the current test session</source>
         <target state="translated">為目前的測試工作階段產生獨立式 HTML 報告</target>
diff --git a/test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/HelpInfoAllExtensionsTests.cs b/test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/HelpInfoAllExtensionsTests.cs
index 16ec65ffd8..7947d7bdc7 100644
--- a/test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/HelpInfoAllExtensionsTests.cs
+++ b/test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/HelpInfoAllExtensionsTests.cs
@@ -135,7 +135,9 @@ Override the Azure DevOps artifact container name. Defaults to 'TestResults_{ass
     --report-html
         Enable generating an HTML report
     --report-html-filename
-        The name of the generated HTML report
+        The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+        Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+        Example: MyReport_{tfm}.html
     --report-trx
         Enable generating TRX report
     --report-trx-filename
@@ -457,7 +459,9 @@ Default type is 'Full'
       --report-html-filename
         Arity: 1
         Hidden: False
-        Description: The name of the generated HTML report
+        Description: The name of the generated HTML report. May include a relative or absolute path; relative paths are resolved against the test results directory and missing directories are created.
+        Supports the following placeholders: {pname} (test application name), {pid} (process ID), {asm} (entry assembly name), {tfm} (target framework moniker), {time} (timestamp).
+        Example: MyReport_{tfm}.html
   MSBuildCommandLineProvider
     Name: MSBuildCommandLineProvider
     Version: *
diff --git a/test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/HtmlReportTests.cs b/test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/HtmlReportTests.cs
index b0aa16bc58..2beb8c0858 100644
--- a/test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/HtmlReportTests.cs
+++ b/test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/HtmlReportTests.cs
@@ -82,15 +82,29 @@ public async Task Html_WhenReportHtmlFilenameIsSpecified_HtmlReportIsGeneratedWi
 
     [DynamicData(nameof(TargetFrameworks.AllForDynamicData), typeof(TargetFrameworks))]
     [TestMethod]
-    public async Task Html_WhenReportHtmlFilenameContainsPath_ErrorIsDisplayed(string tfm)
+    public async Task Html_WhenReportHtmlFilenameContainsPath_HtmlReportIsGeneratedInThatPath(string tfm)
     {
+        string customFileName = Path.Combine("subdir", "report.html");
+        string testResultsPath = Path.Combine(AssetFixture.TargetAssetPath, "bin", "Release", tfm, "TestResults");
+        string customFilePath = Path.Combine(testResultsPath, customFileName);
+        string expectedFilePath = Regex.Escape(customFilePath);
+
         var testHost = TestInfrastructure.TestHost.LocateFrom(AssetFixture.TargetAssetPath, TestAssetFixture.AssetName, tfm);
         TestHostResult testHostResult = await testHost.ExecuteAsync(
-            $"--report-html --report-html-filename {Path.Combine("subdir", "report.html")}",
+            $"--report-html --report-html-filename {customFileName}",
             cancellationToken: TestContext.CancellationToken);
 
-        testHostResult.AssertExitCodeIs(ExitCode.InvalidCommandLine);
-        testHostResult.AssertOutputContains("file name argument must not contain a path or invalid characters");
+        testHostResult.AssertExitCodeIs(ExitCode.Success);
+
+        string outputPattern = $"""
+  In process file artifacts produced:
+    - {expectedFilePath}
+""";
+        testHostResult.AssertOutputMatchesRegex(outputPattern);
+
+        Assert.IsTrue(
+            File.Exists(customFilePath),
+            $"Expected custom HTML report file '{customFileName}' was not found in '{testResultsPath}'.");
     }
 
     [DynamicData(nameof(TargetFrameworks.AllForDynamicData), typeof(TargetFrameworks))]
diff --git a/test/UnitTests/Microsoft.Testing.Extensions.UnitTests/HtmlReportEngineTests.cs b/test/UnitTests/Microsoft.Testing.Extensions.UnitTests/HtmlReportEngineTests.cs
index 7fae073d0e..371a06c49e 100644
--- a/test/UnitTests/Microsoft.Testing.Extensions.UnitTests/HtmlReportEngineTests.cs
+++ b/test/UnitTests/Microsoft.Testing.Extensions.UnitTests/HtmlReportEngineTests.cs
@@ -332,6 +332,117 @@ public async Task GenerateReportAsync_DefaultFileName_IncludesModuleNameAndTarge
         Assert.IsTrue(Regex.IsMatch(Path.GetFileName(finalPath), ExpectedFileNamePattern));
     }
 
+    [TestMethod]
+    public async Task GenerateReportAsync_ExplicitRelativePath_IsResolvedUnderResultsDirectory()
+    {
+        string[]? htmlFileName = [Path.Combine("nested", "custom.html")];
+        _ = _commandLineOptionsMock.Setup(_ => _.TryGetOptionArgumentList(HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName, out htmlFileName)).Returns(true);
+
+        string? pathSeen = null;
+        var directories = new List<string>();
+        _ = _fileSystem.Setup(x => x.ExistFile(It.IsAny<string>())).Returns(false);
+        _ = _fileSystem.Setup(x => x.CreateDirectory(It.IsAny<string>()))
+            .Callback<string>(directories.Add)
+            .Returns<string>(path => path);
+        _ = _fileSystem.Setup(x => x.NewFileStream(It.IsAny<string>(), FileMode.Create))
+            .Returns<string, FileMode>((path, _) =>
+            {
+                pathSeen = path;
+                return new MemoryFileStream();
+            });
+
+        HtmlReportEngine engine = CreateEngine();
+        _ = _configurationMock.SetupGet(_ => _[It.IsAny<string>()]).Returns("out");
+
+        (string finalPath, _) = await engine.GenerateReportAsync([Captured("a", "A", "passed")]);
+
+        string expectedPath = Path.Combine("out", "nested", "custom.html");
+        Assert.AreEqual(expectedPath, finalPath);
+        Assert.AreEqual(expectedPath, pathSeen);
+        Assert.Contains(Path.Combine("out", "nested"), directories);
+    }
+
+    [TestMethod]
+    public async Task GenerateReportAsync_ExplicitAbsolutePath_OverridesResultsDirectory()
+    {
+        string absolutePath = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName() + ".html");
+        string[]? htmlFileName = [absolutePath];
+        _ = _commandLineOptionsMock.Setup(_ => _.TryGetOptionArgumentList(HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName, out htmlFileName)).Returns(true);
+
+        string? pathSeen = null;
+        _ = _fileSystem.Setup(x => x.ExistFile(It.IsAny<string>())).Returns(false);
+        _ = _fileSystem.Setup(x => x.CreateDirectory(It.IsAny<string>())).Returns<string>(path => path);
+        _ = _fileSystem.Setup(x => x.NewFileStream(It.IsAny<string>(), FileMode.Create))
+            .Returns<string, FileMode>((path, _) =>
+            {
+                pathSeen = path;
+                return new MemoryFileStream();
+            });
+
+        HtmlReportEngine engine = CreateEngine();
+        _ = _configurationMock.SetupGet(_ => _[It.IsAny<string>()]).Returns("out");
+
+        (string finalPath, _) = await engine.GenerateReportAsync([Captured("a", "A", "passed")]);
+
+        Assert.AreEqual(absolutePath, finalPath);
+        Assert.AreEqual(absolutePath, pathSeen);
+    }
+
+    [TestMethod]
+    public async Task GenerateReportAsync_ExplicitFileName_ResolvesPlaceholdersAndSanitizesLeafName()
+    {
+        string[]? htmlFileName = [Path.Combine("nested", "report*_{pid}_{tfm}.html")];
+        _ = _commandLineOptionsMock.Setup(_ => _.TryGetOptionArgumentList(HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName, out htmlFileName)).Returns(true);
+
+        string? pathSeen = null;
+        _ = _fileSystem.Setup(x => x.ExistFile(It.IsAny<string>())).Returns(false);
+        _ = _fileSystem.Setup(x => x.CreateDirectory(It.IsAny<string>())).Returns<string>(path => path);
+        _ = _fileSystem.Setup(x => x.NewFileStream(It.IsAny<string>(), FileMode.Create))
+            .Returns<string, FileMode>((path, _) =>
+            {
+                pathSeen = path;
+                return new MemoryFileStream();
+            });
+
+        HtmlReportEngine engine = CreateEngine();
+        _ = _configurationMock.SetupGet(_ => _[It.IsAny<string>()]).Returns("out");
+        _ = _environmentMock.SetupGet(_ => _.ProcessId).Returns(1234);
+
+        (string finalPath, _) = await engine.GenerateReportAsync([Captured("a", "A", "passed")]);
+
+        Assert.AreEqual(pathSeen, finalPath);
+        string finalFileName = Path.GetFileName(finalPath);
+        Assert.StartsWith("report__", finalFileName);
+        Assert.Contains("1234", finalFileName);
+        Assert.Contains("_net", finalFileName);
+        Assert.EndsWith(".html", finalPath);
+    }
+
+    [TestMethod]
+    public async Task GenerateReportAsync_ExplicitReservedFileName_SanitizesLeafName()
+    {
+        string[]? htmlFileName = [Path.Combine("nested", "CON.html")];
+        _ = _commandLineOptionsMock.Setup(_ => _.TryGetOptionArgumentList(HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName, out htmlFileName)).Returns(true);
+
+        string? pathSeen = null;
+        _ = _fileSystem.Setup(x => x.ExistFile(It.IsAny<string>())).Returns(false);
+        _ = _fileSystem.Setup(x => x.CreateDirectory(It.IsAny<string>())).Returns<string>(path => path);
+        _ = _fileSystem.Setup(x => x.NewFileStream(It.IsAny<string>(), FileMode.Create))
+            .Returns<string, FileMode>((path, _) =>
+            {
+                pathSeen = path;
+                return new MemoryFileStream();
+            });
+
+        HtmlReportEngine engine = CreateEngine();
+        _ = _configurationMock.SetupGet(_ => _[It.IsAny<string>()]).Returns("out");
+
+        (string finalPath, _) = await engine.GenerateReportAsync([Captured("a", "A", "passed")]);
+
+        Assert.AreEqual(pathSeen, finalPath);
+        Assert.AreEqual("_CON.html", Path.GetFileName(finalPath));
+    }
+
     [TestMethod]
     public async Task GenerateReportAsync_AppendsDisambiguatingSuffix_When_DefaultFileExists()
     {
@@ -476,6 +587,11 @@ private HtmlReportEngine CreateEngine(MemoryFileStream stream)
         _ = _fileSystem.Setup(x => x.ExistFile(It.IsAny<string>())).Returns(false);
         _ = _fileSystem.Setup(x => x.NewFileStream(It.IsAny<string>(), It.IsAny<FileMode>())).Returns(stream);
 
+        return CreateEngine();
+    }
+
+    private HtmlReportEngine CreateEngine()
+    {
         _ = _configurationMock.SetupGet(_ => _[It.IsAny<string>()]).Returns(string.Empty);
         _ = _environmentMock.SetupGet(_ => _.MachineName).Returns("MachineName");
         _ = _environmentMock.Setup(_ => _.GetEnvironmentVariable(It.IsAny<string>())).Returns("user");
diff --git a/test/UnitTests/Microsoft.Testing.Extensions.UnitTests/HtmlReportGeneratorCommandLineTests.cs b/test/UnitTests/Microsoft.Testing.Extensions.UnitTests/HtmlReportGeneratorCommandLineTests.cs
index 1cace2d6f0..aa4fc14998 100644
--- a/test/UnitTests/Microsoft.Testing.Extensions.UnitTests/HtmlReportGeneratorCommandLineTests.cs
+++ b/test/UnitTests/Microsoft.Testing.Extensions.UnitTests/HtmlReportGeneratorCommandLineTests.cs
@@ -11,13 +11,45 @@ namespace Microsoft.Testing.Extensions.UnitTests;
 public sealed class HtmlReportGeneratorCommandLineTests
 {
     [TestMethod]
-    public async Task IsValid_If_PureHtmlFileName_Is_Provided()
+    [DataRow("report.html")]
+    [DataRow("sub/report.html")]
+    public async Task IsValid_If_HtmlFileNameOrNestedRelativePath_Is_Provided(string fileName)
+    {
+        var provider = new HtmlReportGeneratorCommandLine();
+        Platform.Extensions.CommandLine.CommandLineOption option = provider.GetCommandLineOptions()
+            .First(x => x.Name == HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName);
+
+        ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, [fileName]).ConfigureAwait(false);
+
+        Assert.IsTrue(result.IsValid);
+        Assert.IsTrue(string.IsNullOrEmpty(result.ErrorMessage));
+    }
+
+    [TestMethod]
+    [OSCondition(OperatingSystems.Windows)]
+    public async Task IsValid_If_HtmlFileNameUsesBackslashSeparator_OnWindows()
     {
+        // The '\' character is only a directory separator on Windows; on Unix it would be treated
+        // as part of the leaf file name (and later sanitized at write time).
         var provider = new HtmlReportGeneratorCommandLine();
         Platform.Extensions.CommandLine.CommandLineOption option = provider.GetCommandLineOptions()
             .First(x => x.Name == HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName);
 
-        ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, ["report.html"]).ConfigureAwait(false);
+        ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, ["sub\\report.html"]).ConfigureAwait(false);
+
+        Assert.IsTrue(result.IsValid);
+        Assert.IsTrue(string.IsNullOrEmpty(result.ErrorMessage));
+    }
+
+    [TestMethod]
+    public async Task IsValid_If_HtmlFile_Has_Absolute_Path()
+    {
+        var provider = new HtmlReportGeneratorCommandLine();
+        Platform.Extensions.CommandLine.CommandLineOption option = provider.GetCommandLineOptions()
+            .First(x => x.Name == HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName);
+        string fileName = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName() + ".html");
+
+        ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, [fileName]).ConfigureAwait(false);
 
         Assert.IsTrue(result.IsValid);
         Assert.IsTrue(string.IsNullOrEmpty(result.ErrorMessage));
@@ -40,15 +72,43 @@ public async Task IsInvalid_If_FileName_Does_Not_End_With_Html(string fileName)
     }
 
     [TestMethod]
-    [DataRow("sub/report.html")]
-    [DataRow("sub\\report.html")]
-    [DataRow("..\\report.html")]
     [DataRow("../report.html")]
-    [DataRow("..report.html")] // contains ".."
-    [DataRow("C:report.html")] // drive letter
-    [DataRow(" report.html")] // leading whitespace
-    [DataRow("report.html ")] // trailing whitespace
-    public async Task IsInvalid_If_FileName_Contains_Path_Or_Invalid_Chars(string fileName)
+    [DataRow("nested/../report.html")]
+    public async Task IsInvalid_If_RelativePath_Contains_ParentDirectorySegment(string fileName)
+    {
+        var provider = new HtmlReportGeneratorCommandLine();
+        Platform.Extensions.CommandLine.CommandLineOption option = provider.GetCommandLineOptions()
+            .First(x => x.Name == HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName);
+
+        ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, [fileName]).ConfigureAwait(false);
+
+        Assert.IsFalse(result.IsValid);
+        Assert.AreEqual(HtmlReport.Resources.ExtensionResources.HtmlReportFileNameRelativePathMustStayUnderResultsDirectory, result.ErrorMessage);
+    }
+
+    [TestMethod]
+    [OSCondition(OperatingSystems.Windows)]
+    public async Task IsInvalid_If_HtmlFile_Uses_DriveRelativePath_OnWindows()
+    {
+        // Drive-relative paths such as "C:report.html" are "rooted" but not fully qualified, so they
+        // would silently escape the test results directory. Validate that they are rejected on Windows.
+        // On non-Windows OSes ':' is a valid file-name character, so this check is Windows-only and
+        // matches the TRX option behavior.
+        var provider = new HtmlReportGeneratorCommandLine();
+        Platform.Extensions.CommandLine.CommandLineOption option = provider.GetCommandLineOptions()
+            .First(x => x.Name == HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName);
+
+        ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, ["C:report.html"]).ConfigureAwait(false);
+
+        Assert.IsFalse(result.IsValid);
+        Assert.AreEqual(HtmlReport.Resources.ExtensionResources.HtmlReportFileNameRelativePathMustStayUnderResultsDirectory, result.ErrorMessage);
+    }
+
+    [TestMethod]
+    [DataRow(" ")]
+    [DataRow("sub/")]
+    [DataRow("sub/ ")]
+    public async Task IsInvalid_If_FileNamePart_Is_Empty_Or_Whitespace(string fileName)
     {
         var provider = new HtmlReportGeneratorCommandLine();
         Platform.Extensions.CommandLine.CommandLineOption option = provider.GetCommandLineOptions()
@@ -57,7 +117,20 @@ public async Task IsInvalid_If_FileName_Contains_Path_Or_Invalid_Chars(string fi
         ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, [fileName]).ConfigureAwait(false);
 
         Assert.IsFalse(result.IsValid);
-        Assert.AreEqual(HtmlReport.Resources.ExtensionResources.HtmlReportFileNameShouldNotContainPath, result.ErrorMessage);
+        Assert.AreEqual(HtmlReport.Resources.ExtensionResources.HtmlReportFileNameMustNotBeEmpty, result.ErrorMessage);
+    }
+
+    [TestMethod]
+    public async Task IsInvalid_If_No_Argument_Provided()
+    {
+        var provider = new HtmlReportGeneratorCommandLine();
+        Platform.Extensions.CommandLine.CommandLineOption option = provider.GetCommandLineOptions()
+            .First(x => x.Name == HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName);
+
+        ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, []).ConfigureAwait(false);
+
+        Assert.IsFalse(result.IsValid);
+        Assert.AreEqual(HtmlReport.Resources.ExtensionResources.HtmlReportFileNameMustNotBeEmpty, result.ErrorMessage);
     }
 
     [TestMethod]
@@ -106,33 +179,9 @@ public async Task IsValid_When_HtmlReport_Used_Alone()
     }
 
     [TestMethod]
-    [DataRow("report*.html")] // * is Windows-invalid even though Linux allows it
-    [DataRow("report?.html")] // ? same
-    [DataRow("report\".html")]
-    [DataRow("report<.html")]
-    [DataRow("report>.html")]
-    [DataRow("report|.html")]
-    public async Task IsInvalid_When_FileName_Contains_WindowsInvalidChars_OnAnyOS(string fileName)
-    {
-        var provider = new HtmlReportGeneratorCommandLine();
-        Platform.Extensions.CommandLine.CommandLineOption option = provider.GetCommandLineOptions()
-            .First(x => x.Name == HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName);
-
-        ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, [fileName]).ConfigureAwait(false);
-
-        Assert.IsFalse(result.IsValid);
-        Assert.AreEqual(HtmlReport.Resources.ExtensionResources.HtmlReportFileNameShouldNotContainPath, result.ErrorMessage);
-    }
-
-    [TestMethod]
+    [DataRow("report*.html")]
     [DataRow("CON.html")]
-    [DataRow("con.html")] // case insensitive
-    [DataRow("NUL.html")]
-    [DataRow("PRN.html")]
-    [DataRow("AUX.html")]
-    [DataRow("COM1.html")]
-    [DataRow("LPT9.html")]
-    public async Task IsInvalid_When_FileName_Is_Reserved_Windows_Device_Name(string fileName)
+    public async Task IsValid_When_FileName_WillBeSanitized_AtWriteTime(string fileName)
     {
         var provider = new HtmlReportGeneratorCommandLine();
         Platform.Extensions.CommandLine.CommandLineOption option = provider.GetCommandLineOptions()
@@ -140,20 +189,6 @@ public async Task IsInvalid_When_FileName_Is_Reserved_Windows_Device_Name(string
 
         ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, [fileName]).ConfigureAwait(false);
 
-        Assert.IsFalse(result.IsValid);
-        Assert.AreEqual(HtmlReport.Resources.ExtensionResources.HtmlReportFileNameShouldNotContainPath, result.ErrorMessage);
-    }
-
-    [TestMethod]
-    public async Task IsValid_When_FileName_Starts_With_Reserved_Name_But_Has_Extra_Chars()
-    {
-        // "CONfig.html" is not a reserved device name (only the bare "CON" base name is).
-        var provider = new HtmlReportGeneratorCommandLine();
-        Platform.Extensions.CommandLine.CommandLineOption option = provider.GetCommandLineOptions()
-            .First(x => x.Name == HtmlReportGeneratorCommandLine.HtmlReportFileNameOptionName);
-
-        ValidationResult result = await provider.ValidateOptionArgumentsAsync(option, ["CONfig.html"]).ConfigureAwait(false);
-
         Assert.IsTrue(result.IsValid);
     }
 }