name	documentation-writing
description	Guide for writing clear, comprehensive technical documentation including README files, API docs, guides, and inline documentation

Technical Documentation Writing

This skill activates when writing or improving technical documentation, including README files, API documentation, user guides, and inline code documentation.

When to Use This Skill

Activate when:

Writing README files
Creating API documentation
Writing user guides or tutorials
Documenting code with comments or docstrings
Creating architecture or design documents
Writing changelogs or release notes

README Files

Essential README Structure

Every README should include:

# Project Name

Brief one-liner description of the project.

## Overview

2-3 paragraphs explaining what the project does, why it exists, and who it's for.

## Features

- Key feature 1
- Key feature 2
- Key feature 3

## Installation

### Prerequisites

- Requirement 1 (with version)
- Requirement 2 (with version)

### Install Steps

```bash
# Clone repository
git clone https://github.com/user/project.git
cd project

# Install dependencies
npm install  # or pip install -r requirements.txt, mix deps.get, etc.

# Configure
cp .env.example .env
# Edit .env with your settings

# Run
npm start

Quick Start

# Minimal example to get started
npm start

Usage

Basic Example

// Clear, runnable example
const example = new Project()
example.doSomething()

Advanced Usage

More complex examples with explanations.

Configuration

Option	Type	Default	Description
`apiKey`	string	-	API key for authentication
`timeout`	number	5000	Request timeout in ms

API Reference

Link to detailed API documentation or include core APIs here.

Development

Setup Development Environment

# Development-specific setup
npm install --dev
npm run setup

Running Tests

npm test
npm run test:coverage

Building

npm run build

Contributing

Please read CONTRIBUTING.md for details on our code of conduct and the process for submitting pull requests.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

Credits
Inspirations
Related projects

Support

Documentation: https://docs.example.com
Issues: https://github.com/user/project/issues
Discussions: https://github.com/user/project/discussions


### README Best Practices

- **Start with a clear one-liner**: Immediately tell readers what the project does
- **Include badges**: Build status, coverage, version, license
- **Show, don't tell**: Use code examples liberally
- **Keep it scannable**: Use headers, lists, and code blocks
- **Make examples runnable**: Readers should be able to copy-paste and run
- **Include visual aids**: Screenshots, diagrams, GIFs when appropriate
- **Update regularly**: Keep documentation in sync with code
- **Think about newcomers**: Write for someone seeing the project for the first time

## API Documentation

### Documenting Functions

**Elixir (@doc):**
```elixir
@doc """
Calculates the sum of two numbers.

## Parameters

- `a` - The first number (integer or float)
- `b` - The second number (integer or float)

## Returns

The sum of `a` and `b`.

## Examples

    iex> Math.add(2, 3)
    5

    iex> Math.add(2.5, 3.7)
    6.2

"""
@spec add(number(), number()) :: number()
def add(a, b) do
  a + b
end

JavaScript (JSDoc):

/**
 * Calculates the sum of two numbers.
 *
 * @param {number} a - The first number
 * @param {number} b - The second number
 * @returns {number} The sum of a and b
 *
 * @example
 * add(2, 3)
 * // => 5
 */
function add(a, b) {
  return a + b
}

Python (docstring):

def add(a: float, b: float) -> float:
    """
    Calculate the sum of two numbers.

    Args:
        a: The first number
        b: The second number

    Returns:
        The sum of a and b

    Examples:
        >>> add(2, 3)
        5
        >>> add(2.5, 3.7)
        6.2

    Raises:
        TypeError: If arguments are not numbers
    """
    return a + b

Rust (doc comments):

/// Calculates the sum of two numbers.
///
/// # Arguments
///
/// * `a` - The first number
/// * `b` - The second number
///
/// # Returns
///
/// The sum of `a` and `b`
///
/// # Examples
///
/// ```
/// use mylib::add;
///
/// assert_eq!(add(2, 3), 5);
/// assert_eq!(add(2.5, 3.7), 6.2);
/// ```
pub fn add(a: f64, b: f64) -> f64 {
    a + b
}

Module/Class Documentation

Document the purpose, usage, and public API:

defmodule MyApp.UserManager do
  @moduledoc """
  Manages user accounts and authentication.

  The UserManager provides functions for creating, updating, and authenticating
  users. It handles password hashing, session management, and user validation.

  ## Usage

      # Create a new user
      {:ok, user} = UserManager.create_user(%{
        email: "alice@example.com",
        password: "secure_password"
      })

      # Authenticate
      {:ok, user} = UserManager.authenticate("alice@example.com", "secure_password")

      # Update user
      {:ok, updated} = UserManager.update_user(user, %{name: "Alice Smith"})

  ## Configuration

  Configure in `config/config.exs`:

      config :my_app, MyApp.UserManager,
        password_min_length: 8,
        session_timeout: 3600

  """
end

API Endpoint Documentation

Document RESTful APIs clearly:

## Endpoints

### Create User

Creates a new user account.

**Endpoint:** `POST /api/users`

**Authentication:** Not required

**Request Body:**

```json
{
  "email": "alice@example.com",
  "password": "secure_password",
  "name": "Alice Smith"
}

Response (201 Created):

{
  "id": "123",
  "email": "alice@example.com",
  "name": "Alice Smith",
  "created_at": "2024-01-15T10:30:00Z"
}

Error Responses:

400 Bad Request - Invalid input

{
  "error": "validation_error",
  "details": {
    "email": ["must be a valid email address"],
    "password": ["must be at least 8 characters"]
  }
}

409 Conflict - Email already exists

{
  "error": "email_taken",
  "message": "An account with this email already exists"
}

Example:

curl -X POST https://api.example.com/users \
  -H "Content-Type: application/json" \
  -d '{
    "email": "alice@example.com",
    "password": "secure_password",
    "name": "Alice Smith"
  }'


## User Guides and Tutorials

### Tutorial Structure

```markdown
# Tutorial: Building Your First [Feature]

## What You'll Build

Brief description of the end result.

## Prerequisites

- Knowledge requirement 1
- Installed tool 1
- Account/access requirement

## Step 1: [First Major Step]

Explanation of what we're doing and why.

```language
// Code for this step

What's happening here:

Explanation of key line 1
Explanation of key line 2

Step 2: [Next Step]

Continue with incremental steps...

Testing

How to verify it works.

Next Steps

Related tutorial 1
Advanced topic 1
Further reading


### Tutorial Best Practices

- **Show working code first**: Let readers see the goal before diving into details
- **Explain the 'why'**: Don't just show what to do, explain reasoning
- **Incremental steps**: Each step should build on the previous
- **Include checkpoints**: Ways to verify progress
- **Provide complete code**: Include a repository or final code snippet
- **Anticipate problems**: Address common mistakes
- **Link to references**: Point to relevant API docs and resources

## Inline Code Documentation

### When to Write Comments

**DO write comments for:**
- Complex algorithms or business logic
- Non-obvious decisions ("why" not "what")
- Workarounds for bugs or limitations
- Public APIs and exported functions
- Configuration and constants

**DON'T write comments for:**
- Obvious code
- What the code does (prefer clear naming)
- Outdated information
- Commented-out code (use version control)

### Good Comment Examples

```elixir
# Good: Explains WHY
# Use exponential backoff to avoid overwhelming the API after rate limit errors
defp retry_with_backoff(attempt) do
  :timer.sleep(:math.pow(2, attempt) * 1000)
end

# Bad: Explains WHAT (obvious from code)
# Multiply 2 to the power of attempt and multiply by 1000
defp retry_with_backoff(attempt) do
  :timer.sleep(:math.pow(2, attempt) * 1000)
end

# Good: Documents workaround
# NOTE: Using String.to_existing_atom because the Erlang VM limits atoms to ~1M.
# All valid status atoms are pre-defined in this module.
def parse_status(status_string) do
  String.to_existing_atom(status_string)
end

# Good: Explains business rule
# Users must be at least 13 years old per COPPA regulations
@minimum_age 13

Architecture Documentation

Architecture Decision Records (ADR)

Document significant architectural decisions:

# ADR 001: Use PostgreSQL for Primary Database

## Status

Accepted

## Context

We need to choose a database for our application that supports:
- ACID transactions
- Complex queries with joins
- JSON data storage
- Full-text search
- Horizontal scalability (future requirement)

## Decision

We will use PostgreSQL as our primary database.

## Consequences

### Positive

- Mature, stable, well-documented
- Excellent JSON support with JSONB
- Built-in full-text search
- Strong consistency guarantees
- Large ecosystem of tools and extensions
- Can scale with read replicas and partitioning

### Negative

- More complex to operate than simpler databases
- Vertical scaling has limits (though sufficient for our needs)
- Requires more server resources than lighter alternatives

### Neutral

- Team needs to learn PostgreSQL-specific features
- May need to hire PostgreSQL expertise as we scale

## Alternatives Considered

- **MySQL**: Weaker JSON support, less feature-rich
- **MongoDB**: No ACID guarantees, eventual consistency issues
- **SQLite**: Not suitable for multi-user web applications

Changelog Documentation

Follow Keep a Changelog format:

# Changelog

All notable changes to this project will be documented in this file.

The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).

## [Unreleased]

### Added
- New feature in development

## [1.2.0] - 2024-01-15

### Added
- User profile pictures
- Email notification preferences
- Dark mode support

### Changed
- Improved search performance by 40%
- Updated UI to match new brand guidelines

### Fixed
- Login redirect loop on Safari
- Memory leak in background sync process

### Deprecated
- Old `/v1/users` endpoint (use `/v2/users` instead)

## [1.1.0] - 2024-01-01

### Added
- Two-factor authentication
- Export user data to JSON

### Security
- Fixed XSS vulnerability in comment rendering

## [1.0.0] - 2023-12-15

### Added
- Initial release
- User registration and authentication
- Basic user profiles

Documentation Tools

Documentation Generators

Elixir: ExDoc - mix docs
JavaScript: JSDoc, TypeDoc
Python: Sphinx, MkDocs
Rust: rustdoc - cargo doc
Static sites: VitePress, Docusaurus, GitBook

Diagram Tools

Mermaid: Diagrams in Markdown

```mermaid
graph TD
    A[User] -->|Requests| B[Load Balancer]
    B --> C[Web Server 1]
    B --> D[Web Server 2]
    C --> E[Database]
    D --> E

PlantUML: UML diagrams as code
Excalidraw: Hand-drawn style diagrams
Draw.io: Flowcharts and diagrams

Documentation Style Guide

Writing Style

Use active voice: "The function returns" not "The value is returned"
Be concise: Remove unnecessary words
Use present tense: "Returns" not "Will return"
Be specific: "Timeout in milliseconds" not "Timeout value"
Avoid jargon: Or explain it when necessary
Use examples: Show, don't just tell

Formatting Conventions

Code: Use backticks for inline code
Commands: Show with $ prefix or in code blocks
File paths: Use code formatting
Emphasis: Use bold for important points, italic for slight emphasis
Lists: Use bullets for unordered, numbers for sequential steps
Headers: Use sentence case, not title case

Code Examples

Complete: Include all necessary imports and setup
Runnable: Readers should be able to copy and run
Realistic: Use meaningful variable names and realistic data
Commented: Explain non-obvious parts
Tested: Ensure examples actually work
Current: Keep in sync with latest API

Documentation Maintenance

Keeping Docs Updated

Update documentation in the same PR as code changes
Review docs during code review
Set up doc linting (broken links, outdated examples)
Schedule regular documentation audits
Use version tags in examples when API changes
Mark deprecated features clearly

Documentation Testing

# Elixir doctests - examples in docs are actual tests
defmodule Math do
  @doc """
  Adds two numbers.

  ## Examples

      iex> Math.add(2, 3)
      5

  """
  def add(a, b), do: a + b
end

/// Adds two numbers.
///
/// # Examples
///
/// ```
/// assert_eq!(add(2, 3), 5);
/// ```
pub fn add(a: i32, b: i32) -> i32 {
    a + b
}

Key Principles

Write for your audience: Tailor complexity to reader's experience level
Show examples: Code examples are worth a thousand words
Keep it current: Outdated docs are worse than no docs
Make it scannable: Use headers, lists, code blocks, and white space
Explain the 'why': Help readers understand reasoning, not just steps
Start simple: Begin with quickstart, then go deeper
Test documentation: Ensure examples run and links work
Iterate based on feedback: Improve based on user questions and confusion

documentation-writing

Install Skill

SKILL.md