code-documentation

What this skill does

# Code Documentation Skill

## Overview

This skill generates professional, comprehensive documentation for software projects, codebases, libraries, and APIs. It follows industry best practices from projects like React, Django, Stripe, and Kubernetes to produce documentation that is accurate, well-structured, and useful for both new contributors and experienced developers.

The output ranges from single-file READMEs to multi-document developer guides, always matched to the project's complexity and the user's needs.

## Core Capabilities

- Generate comprehensive README.md files with badges, installation, usage, and API reference
- Create API reference documentation from source code analysis
- Produce architecture and design documentation with diagrams
- Write developer onboarding and contribution guides
- Generate changelogs from commit history or release notes
- Create inline code documentation following language-specific conventions
- Support JSDoc, docstrings, GoDoc, Javadoc, and Rustdoc formats
- Adapt documentation style to the project's language and ecosystem

## When to Use This Skill

**Always load this skill when:**

- User asks to "document", "create docs", or "write documentation" for any code
- User requests a README, API reference, or developer guide
- User shares a codebase or repository and wants documentation generated
- User asks to improve or update existing documentation
- User needs architecture documentation, including diagrams
- User requests a changelog or migration guide

## Documentation Workflow

### Phase 1: Codebase Analysis

Before writing any documentation, thoroughly understand the codebase.

#### Step 1.1: Project Discovery

Identify the project fundamentals:

| Field | How to Determine |
|-------|-----------------|
| **Language(s)** | Check file extensions, `package.json`, `pyproject.toml`, `go.mod`, `Cargo.toml`, etc. |
| **Framework** | Look at dependencies for known frameworks (React, Django, Express, Spring, etc.) |
| **Build System** | Check for `Makefile`, `CMakeLists.txt`, `webpack.config.js`, `build.gradle`, etc. |
| **Package Manager** | npm/yarn/pnpm, pip/uv/poetry, cargo, go modules, etc. |
| **Project Structure** | Map out the directory tree to understand the architecture |
| **Entry Points** | Find main files, CLI entry points, exported modules |
| **Existing Docs** | Check for existing README, docs/, wiki, or inline documentation |

#### Step 1.2: Code Structure Analysis

Use sandbox tools to explore the codebase:

```bash
# Get directory structure
ls /mnt/user-data/uploads/project-dir/

# Read key files
read_file /mnt/user-data/uploads/project-dir/package.json
read_file /mnt/user-data/uploads/project-dir/pyproject.toml

# Search for public API surfaces
grep -r "export " /mnt/user-data/uploads/project-dir/src/
grep -r "def " /mnt/user-data/uploads/project-dir/src/ --include="*.py"
grep -r "func " /mnt/user-data/uploads/project-dir/ --include="*.go"
```

#### Step 1.3: Identify Documentation Scope

Based on analysis, determine what documentation to produce:

| Project Size | Recommended Documentation |
|-------------|--------------------------|
| **Single file / script** | Inline comments + usage header |
| **Small library** | README with API reference |
| **Medium project** | README + API docs + examples |
| **Large project** | README + Architecture + API + Contributing + Changelog |

### Phase 2: Documentation Generation

#### Step 2.1: README Generation

Every project needs a README. Follow this structure:

```markdown
# Project Name

[One-line project description — what it does and why it matters]

[![Badge](link)](#) [![Badge](link)](#)

## Features

- [Key feature 1 — brief description]
- [Key feature 2 — brief description]
- [Key feature 3 — brief description]

## Quick Start

### Prerequisites

- [Prerequisite 1 with version requirement]
- [Prerequisite 2 with version requirement]

### Installation

[Installation commands with copy-paste-ready code blocks]

### Basic Usage

[Minimal working example that demonstrates core functionality]

## Documentation

- [Link to full API reference if separate]
- [Link to architecture docs if separate]
- [Link to examples directory if applicable]

## API Reference

[Inline API reference for smaller projects OR link to generated docs]

## Configuration

[Environment variables, config files, or runtime options]

## Examples

[2-3 practical examples covering common use cases]

## Development

### Setup

[How to set up a development environment]

### Testing

[How to run tests]

### Building

[How to build the project]

## Contributing

[Contribution guidelines or link to CONTRIBUTING.md]

## License

[License information]
```

#### Step 2.2: API Reference Generation

For each public API surface, document:

**Function / Method Documentation**:

```markdown
### `functionName(param1, param2, options?)`

Brief description of what this function does.

**Parameters:**

| Parameter | Type | Required | Default | Description |
|-----------|------|----------|---------|-------------|
| `param1` | `string` | Yes | — | Description of param1 |
| `param2` | `number` | Yes | — | Description of param2 |
| `options` | `Object` | No | `{}` | Configuration options |
| `options.timeout` | `number` | No | `5000` | Timeout in milliseconds |

**Returns:** `Promise<Result>` — Description of return value

**Throws:**
- `ValidationError` — When param1 is empty
- `TimeoutError` — When the operation exceeds the timeout

**Example:**

\`\`\`javascript
const result = await functionName("hello", 42, { timeout: 10000 });
console.log(result.data);
\`\`\`
```

**Class Documentation**:

```markdown
### `ClassName`

Brief description of the class and its purpose.

**Constructor:**

\`\`\`javascript
new ClassName(config)
\`\`\`

| Parameter | Type | Description |
|-----------|------|-------------|
| `config.option1` | `string` | Description |
| `config.option2` | `boolean` | Description |

**Methods:**

- [`method1()`](#method1) — Brief description
- [`method2(param)`](#method2) — Brief description

**Properties:**

| Property | Type | Description |
|----------|------|-------------|
| `property1` | `string` | Description |
| `property2` | `number` | Read-only. Description |
```

#### Step 2.3: Architecture Documentation

For medium-to-large projects, include architecture documentation:

```markdown
# Architecture Overview

## System Diagram

[Include a Mermaid diagram showing the high-level architecture]

\`\`\`mermaid
graph TD
    A[Client] --> B[API Gateway]
    B --> C[Service A]
    B --> D[Service B]
    C --> E[(Database)]
    D --> E
\`\`\`

## Component Overview

### Component Name
- **Purpose**: What this component does
- **Location**: `src/components/name/`
- **Dependencies**: What it depends on
- **Public API**: Key exports or interfaces

## Data Flow

[Describe how data flows through the system for key operations]

## Design Decisions

### Decision Title
- **Context**: What situation led to this decision
- **Decision**: What was decided
- **Rationale**: Why this approach was chosen
- **Trade-offs**: What was sacrificed
```

#### Step 2.4: Inline Code Documentation

Generate language-appropriate inline documentation:

**Python (Docstrings — Google style)**:
```python
def process_data(input_path: str, options: dict | None = None) -> ProcessResult:
    """Process data from the given file path.

    Reads the input file, applies transformations based on the provided
    options, and returns a structured result object.

    Args:
        input_path: Absolute path to the input data file.
            Supports CSV, JSON, and Parquet formats.
        options: Optional configuration dictionary.
            - "validate" (bool): Enable input validation. Defaults to True.
            - "format" (str): Output format ("json" or "csv"). Defaults to "json".

    Returns:
        A ProcessResult containing the transformed data and metadata.

    Raises:
        FileNotFoundError: If input_path does not ex