Schema type with optional properties

[LucasDemea]

Hi, I'm coding a library where developers will be able to define their own schema, which should extend a certain type.
Every property of this type must be optional.

Is this possible with Typebox ? How can I achieve this ?

I tried this :

type CustomSchema = TObject<{
  foo?: TString;
  bar?: TNumber;
  baz?: TBoolean;
}>;

const schema: CustomSchema = Type.Object({
  foo: Type.String(),
  baz: Type.Boolean(),
});

But I get this error

Type 'TObject<{ foo: TString; baz: TBoolean; }>' is not assignable to type 'TSchema'.
  Types of property 'static' are incompatible.
    Property 'bar' is missing in type '{ foo: string; baz: boolean; }' but required in type '{ foo: string; bar: number; baz: boolean; }'.

[potatohoney-p]

For the @sinclair/typebox 0.34 API, constrain the property map before constructing the object, rather than annotating the result as TObject with optional keys:

import {
  Type,
  type Static,
  type TString,
  type TNumber,
  type TBoolean,
} from '@sinclair/typebox';

type AllowedProperties = {
  foo: TString;
  bar: TNumber;
  baz: TBoolean;
};

const properties = {
  foo: Type.String(),
  baz: Type.Boolean(),
} satisfies Partial<AllowedProperties>;

const schema = Type.Object(properties);
type Data = Static<typeof schema>; // { foo: string; baz: boolean }

bar may be omitted from the schema, while the supplied keys retain their precise types. Using foo: Type.Number() in that object is a compile-time error. satisfies checks the constraint without widening the variable to the entire optional property map.

For a library API that accepts these property definitions and allows additional schema properties, a generic factory preserves the same inference:

import type { TProperties } from '@sinclair/typebox';

function defineSchema<P extends TProperties & Partial<AllowedProperties>>(
  properties: P,
) {
  return Type.Object(properties);
}

const custom = defineSchema({ foo: Type.String(), baz: Type.Boolean() });
// defineSchema({ foo: Type.Number() }); // compile-time error

There are two different meanings of optional here. The above permits developers to leave a property out of the schema definition. Properties they do include are still required in validated data. If the data fields themselves should also be optional, use Type.Partial(schema) (or Type.Optional on individual fields); a TypeScript ? on the property-map type does not create TypeBox's optional marker.

Checked with @sinclair/typebox@0.34.41, TypeScript 5.8.3, strict and exactOptionalPropertyTypes: your original annotation reproduces the missing-bar error, the property-map/factory examples type-check, and runtime checks confirm the selected fields remain required until Type.Partial is applied. This example targets 0.34, not the newer typebox 1.x package.

TypeScript's satisfies documentation describes the inference-preserving check used here.