CodeDrills

Replace mindless scrolling with something actually useful — practice and learn coding, one drill at a time.

Code Drills is a mobile app that delivers bite-sized coding challenges and lessons so you can turn idle moments into real learning.

Pick a language, pick a level, and drill.

No subscriptions, no distractions, just pure coding practice on the go.

This isn't meant to replace building projects - it's for those moments when you can't access your computer but want to keep your coding skills sharp.

your ai-agent is coding fast, better catch up...

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📚 Content Structure

Community-contributed content lives under two top-level directories:

challenges/
  <language>/
    <language>_challenges.json
topics/
  <language>/
    <language>_topics.json
img/
  languages/
    <language>/

Supported Languages

Language	Directory
Python	python/
SQL	sql/
JavaScript	javascript/
Rust	rust/
AI + ML	ai+ml/

Levels

Each file covers four levels:

Level	Description
new	No prior experience assumed
beginner	Basic syntax and concepts
intermediate	Real-world patterns and problem-solving
advanced	Performance, idioms, deeper internals

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🗂️ JSON Schemas

See the examples/ folder for annotated reference files:

• examples/challenge_example.json — challenge format
• examples/lesson_example.json — topic/lesson format
• examples/ai+ml_challenge_example.json — AI + ML challenge format (multiple choice)
• examples/ai+ml_lesson_example.json — AI + ML lesson format with image support

Challenge keys

{
  "language": "python",
  "levels": [
    {
      "level": "new",
      "challenges": [
        {
          "id": "py-new-1",
          "language": "python",
          "level": "new",
          "title": "...",
          "description": "...",
          "starterCode": "...",
          "hint": "...",
          "solution": {
            "code": "...",
            "steps": [
              { "title": "...", "explanation": "..." }
            ]
          }
        }
      ]
    }
  ]
}

For ai+ml challenges, use choices instead of starterCode:

"choices": [
  { "text": "...", "correct": true },
  { "text": "...", "correct": false },
  { "text": "...", "correct": false },
  { "text": "...", "correct": false }
]

Topic keys

{
  "language": "python",
  "levels": [
    {
      "level": "new",
      "topics": [
        {
          "id": "py-new-datatypes",
          "language": "python",
          "level": "new",
          "title": "...",
          "description": "...",
          "estimatedMinutes": 8,
          "lessons": [
            { "title": "...", "body": "...", "code": "...", "runnable": true }
          ]
        }
      ]
    }
  ]
}

For ai+ml lessons, image is supported on each lesson object and lessons with code must set "runnable": false.

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🛠️ Scripts

Local content review UI

The local review UI lets contributors review and update lesson and challenge JSON without editing the raw files by hand.

Launch

Install uv if it is not already available, then run the following from the repository root:

uv run streamlit run content_review.py

Open the local URL printed by Streamlit, normally http://localhost:8501.

What it supports

• Filter lessons and challenges by language, level, topic, and review queue.
• Review source content, edit every existing text field, and save changes directly to its source JSON file.
• Inspect copyable JSON and language-aware code snippets, including each snippet's runnable status.
• Preview lesson images, inspect their paths, and update an image path when needed.
• Mark an item reviewed with or without source changes. Reviewed items are omitted from the default queue and remain available in the Reviewed queue.
• Validate all content JSON after a save.

Review status is stored only in .content-review-state.json, which is ignored by Git and does not alter app content.

scripts/merge_content.py — Build combined output files

This script reads all language-specific challenge and topic JSON files, deduplicates entries by id, and writes two merged files into an output/ directory at the repository root (excluded from version control via .gitignore).

Deduplication rule: if an output file from a previous run already exists, its entries are loaded first and take priority. New entries whose id already appears in the existing output are skipped, so manual edits to the output files are preserved across re-runs.

Usage

# Merge both challenges and lessons (default)
python scripts/merge_content.py

# Merge challenge files only
python scripts/merge_content.py --challenges

# Merge lesson/topic files only
python scripts/merge_content.py --lessons

Output files

File	Contents
output/challenges.json	All challenges from every language, flat list keyed by challenges
output/lessons.json	All topics (with nested lessons) from every language, flat list keyed by topics

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🤝 Contributing

We welcome challenge and topic contributions! Read CONTRIBUTING.md for step-by-step instructions, naming conventions, and the review process.

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🔒 Privacy

See privacy-policy.md.

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📄 License

MIT © Federico Raimondi