Documentation Writing

Write clear, consistent, and maintainable documentation for software projects.

Prerequisites

• Access to the project source code
• Understanding of the project's purpose and structure
• Familiarity with the project's conventions

Documentation Types

1. README Structure

Every project should have a README.md at the root with these sections:

markdown
# Project Name

One-sentence description of what the project does.

## Features

- Feature 1: brief description
- Feature 2: brief description

## Quick Start

### Prerequisites

- Requirement 1
- Requirement 2

### Installation

Installation command

### Usage

Basic usage example

## Configuration

| Variable | Description | Default |
|----------|-------------|---------|
| `VAR_NAME` | What it does | `default` |

## API Reference

Link to detailed API docs or inline summary.

## Contributing

Link to CONTRIBUTING.md or brief guidelines.

## License

License type with link.

Rules:

• Start with a clear, concise project name and tagline
• Provide a "Quick Start" that works in under 30 seconds
• Use real commands, not pseudocode
• Include links to detailed docs for complex topics
• Keep README under 500 lines; move details to separate files

2. API Documentation

Document APIs using these patterns:

REST APIs

markdown
## Endpoints

### POST /api/v1/users

Create a new user account.

**Request:**

{ "email": "user@example.com", "name": "Jane Doe", "role": "member" }

**Response (201 Created):**

{ "id": "usr_abc123", "email": "user@example.com", "name": "Jane Doe", "created_at": "2024-01-15T10:30:00Z" }

**Errors:**

| Status | Code | Description |
|--------|------|-------------|
| 400 | `invalid_email` | Email format is invalid |
| 409 | `email_exists` | Email already registered |

CLI Tools

markdown
## Commands

### `tool init`

Initialize a new project.

**Usage:**

tool init options] <project-name>

**Options:**

| Flag | Description | Default |
|------|-------------|---------|
| `--template, -t` | Template to use | `default` |
| `--yes, -y` | Skip prompts | `false` |

**Examples:**

Initialize with default template

tool init my-project

Initialize with specific template

tool init my-project --template typescript

Function/Method Documentation

markdown
### `createUser(options: CreateUserOptions): Promise<User>`

Creates a new user in the system.

**Parameters:**

- `options.email` (string, required): User's email address
- `options.name` (string, required): User's display name
- `options.role` (enum, optional): User role. One of: `admin`, `member`, `viewer`. Default: `member`

**Returns:** `Promise<User>` - The created user object

**Throws:**

- `ValidationError` - If email is invalid
- `ConflictError` - If email already exists

**Example:**

const user = await createUser({ email: 'jane@example.com', name: 'Jane Doe' });

3. Architecture Decision Records (ADRs)

Use ADRs to document significant architectural decisions. Store in docs/adr/ or docs/decisions/.

ADR Template

markdown
# ADR-{NUMBER}: {TITLE}

## Status

{Proposed | Accepted | Deprecated | Superseded by ADR-XXX}

## Date

{YYYY-MM-DD}

## Context

What is the issue that we're seeing that is motivating this decision or change?

## Decision

What is the change that we're proposing and/or doing?

## Consequences

### Positive

- {benefit 1}
- {benefit 2}

### Negative

- {tradeoff 1}
- {tradeoff 2}

### Risks

- {risk 1}

## Alternatives Considered

### {Alternative 1}

{Description of alternative}

**Pros:** {benefits}
**Cons:** {drawbacks}
**Why rejected:** {reason}

ADR Examples

markdown
# ADR-001: Use PostgreSQL as Primary Database

## Status

Accepted

## Date

2024-01-15

## Context

We need a relational database that supports complex queries, JSON storage, and has strong ecosystem support.

## Decision

We will use PostgreSQL as our primary database.

## Consequences

### Positive

- ACID compliance for transactional data
- Native JSON support for flexible schemas
- Excellent tooling and community support

### Negative

- Heavier operational overhead than SQLite
- Requires dedicated database server

### Risks

- Team needs to learn PostgreSQL-specific features

## Alternatives Considered

### SQLite

**Pros:** Zero config, embedded, fast for read-heavy workloads
**Cons:** Limited concurrency, no network access
**Why rejected:** Doesn't support concurrent writes from multiple services

Rules:

• Number ADRs sequentially: 001, 002, etc.
• Write in clear, factual language
• Record the decision, not just the options
• Document rejected alternatives and why

4. CHANGELOG Format

Follow Keep a Changelog format. File: CHANGELOG.md.

markdown
# Changelog

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

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

## [Unreleased]

### Added
- New feature description

### Changed
- Changes to existing functionality

### Deprecated
- Features that will be removed

### Removed
- Features that have been removed

### Fixed
- Bug fixes

### Security
- Vulnerability fixes

## [1.2.0] - 2024-01-15

### Added
- User authentication with JWT tokens
- Rate limiting on API endpoints

### Fixed
- Memory leak in connection pool
- Incorrect date formatting in exports

## [1.1.0] - 2024-01-01

### Added
- CSV export functionality

### Changed
- Improved query performance by 50%

## [1.0.0] - 2023-12-01

Initial stable release.

Rules:

• Add entries to [Unreleased] section
• Move to versioned section on release
• Use past tense for Fixed/Changed, imperative for Added
• Group by type: Added, Changed, Deprecated, Removed, Fixed, Security
• Include issue/PR references: - Fix login timeout (#123)

5. Inline Documentation

General Principles

• Document why, not what
• Keep comments close to the code they describe
• Update comments when updating code
• Use complete sentences with proper punctuation

When to Comment

go
// GOOD: Explains why
// Retry 3 times because the API intermittently fails under load
for i := 0; i < 3; i++ {
    result, err := callAPI()
    if err == nil {
        return result
    }
}

// BAD: Explains what (code is self-explanatory)
// Loop 3 times
for i := 0; i < 3; i++ {
    // ...
}

Documentation Comments

go
// ProcessOrder handles the complete order lifecycle including payment
// processing, inventory allocation, and shipping notification.
//
// It returns an error if any step fails, but partial side effects
// may have occurred (e.g., payment charged but not shipped).
//
// See: https://docs.internal.com/orders/lifecycle
func ProcessOrder(ctx context.Context, orderID string) error {
    // ...
}

TODO/FIXME Format

typescript
// TODO(username): description [ticket-id]
// FIXME(username): description [ticket-id]
// HACK(username): temporary workaround for #123

// Examples:
// TODO(jane): add retry logic for transient failures [PROJ-456]
// FIXME(bob): remove after API v1 deprecation [PROJ-789]

Style Guidelines

Writing Style

• Use active voice: "The function returns..." not "The value is returned..."
• Use present tense: "This method creates..." not "This method will create..."
• Be concise: Aim for 1-2 sentences per comment
• Use consistent terminology: Pick one term and stick with it

Formatting

• Use Markdown for all documentation files
• Use code blocks for commands, paths, and code
• Use bold for emphasis on key terms
• Use numbered lists for sequential steps
• Use bullet lists for non-sequential items

Structure

• Start with the most important information
• Use headings to break up long sections
• Include a table of contents for docs over 200 lines
• Link to related documentation

Process

1. Identify documentation type needed (README, API, ADR, etc.)
2. Review existing docs for patterns and conventions
3. Write draft following the appropriate template
4. Review for accuracy - test all code examples
5. Proofread - check for typos and clarity
6. Commit with appropriate message type (oth)

Edge Cases

Outdated Documentation

When documentation is outdated:

1. Update the documentation
2. Add an entry to CHANGELOG under [Unreleased] > Fixed
3. Consider if the old documentation should be archived

Conflicting Sources

When documentation conflicts with code:

1. Trust the code as the source of truth
2. Update documentation to match
3. Add tests if the behavior is intentional

Large Documentation Updates

For major documentation overhauls:

1. Break into multiple commits
2. Use ADR if it involves architectural decisions
3. Update CHANGELOG with summary

Examples

Example: Writing a README

Input: User asks "Write a README for my project"

Process:

1. Read package.json, go.mod, or similar to understand the project
2. Review existing source for key features
3. Draft README following the template
4. Include real, tested examples

Output:

markdown
# myproject

A fast, lightweight JSON parser for Go.

## Quick Start

go get github.com/user/myproject

import "github.com/user/myproject"

data, err := myproject.Parse(jsonString)

## Features

- Streaming parser for large files
- Zero allocations in hot path
- Full RFC 8259 compliance

Example: Creating an ADR

Input: User asks "Document why we chose Redis"

Process:

1. Review meeting notes or Slack discussions
2. Identify the context, decision, and tradeoffs
3. Draft ADR using the template
4. Save as docs/adr/003-use-redis-for-caching.md

Best Practices

• Write for your audience: Developers vs users vs operators
• Keep docs close to code: Store with the relevant source
• Version documentation: Tag docs with releases
• Automate what you can: Generate API docs from code annotations
• Review docs in PRs: Treat documentation like code
• Measure usage: Track which docs are accessed

Troubleshooting

Documentation Feels Outdated

• Add a "Last updated: YYYY-MM-DD" header
• Set up reminders to review quarterly
• Consider automating doc generation from code

Too Much Documentation

• Focus on what users need to get started
• Move detailed reference to separate files
• Use links instead of duplicating content

Inconsistent Style

• Create a style guide
• Use linting tools (markdownlint, Vale)
• Review docs in pull requests