documentation-and-adrs

What this skill does

# Documentation and ADRs

## Overview

Document decisions, not just code. The most valuable documentation captures the *why* — the context, constraints, and trade-offs that led to a decision. Code shows *what* was built; documentation explains *why it was built this way* and *what alternatives were considered*.

## Instructions

### Architecture Decision Records (ADRs)

Write an ADR when:
- Choosing a framework, library, or major dependency
- Designing a data model or database schema
- Selecting an authentication or API architecture strategy
- Any decision that would be expensive to reverse

Store ADRs in `docs/decisions/` with sequential numbering:

```markdown
# ADR-001: Use PostgreSQL for primary database

## Status
Accepted | Superseded by ADR-XXX | Deprecated

## Date
2025-01-15

## Context
[Key requirements and constraints that drove the decision]

## Decision
[What was decided and why]

## Alternatives Considered
[Each alternative with pros, cons, and reason for rejection]

## Consequences
[What follows from this decision]
```

**ADR Lifecycle:** `PROPOSED → ACCEPTED → (SUPERSEDED or DEPRECATED)`

Don't delete old ADRs — they capture historical context. When a decision changes, write a new ADR that references and supersedes the old one.

### Inline Documentation

Comment the *why*, not the *what*:

```typescript
// BAD: Restates the code
// Increment counter by 1
counter += 1;

// GOOD: Explains non-obvious intent
// Rate limit uses a sliding window to prevent burst attacks at window edges
if (now - windowStart > WINDOW_SIZE_MS) {
  counter = 0;
  windowStart = now;
}
```

Don't leave TODO comments for things you should just do now. Don't leave commented-out code — git has history.

### API Documentation

For public APIs, document with types:

```typescript
/**
 * Creates a new task.
 * @param input - Task creation data (title required, description optional)
 * @returns The created task with server-generated ID and timestamps
 * @throws {ValidationError} If title is empty or exceeds 200 characters
 * @throws {AuthenticationError} If the user is not authenticated
 */
export async function createTask(input: CreateTaskInput): Promise<Task> {}
```

### README Structure

Every project should cover:
- One-paragraph description
- Quick Start (clone, install, env, run)
- Commands table (dev, test, build, lint)
- Architecture overview with links to ADRs
- Contributing guidelines

### Changelog Maintenance

```markdown
## [1.2.0] - 2025-01-20
### Added
- Task sharing: users can share tasks with team members (#123)
### Fixed
- Duplicate tasks appearing when rapidly clicking create button (#125)
### Changed
- Task list now loads 50 items per page (was 20) (#126)
```

## Examples

### When to Document vs When NOT to

**Document:**
- Making a significant architectural decision
- Choosing between competing approaches
- Adding or changing a public API
- Known gotchas that could trap future developers or agents

**Don't document:**
- Obvious code that's self-explanatory
- Throwaway prototypes
- Comments that restate what the code says

### Document Known Gotchas

```typescript
/**
 * IMPORTANT: Must be called before the first render.
 * If called after hydration, causes a flash of unstyled content
 * because the theme context isn't available during SSR.
 * See ADR-003 for the full design rationale.
 */
export function initializeTheme(theme: Theme): void {}
```

## Guidelines

### Common Rationalizations

| Rationalization | Reality |
|---|---|
| "The code is self-documenting" | Code shows what, not why or what was rejected |
| "We'll write docs when the API stabilizes" | APIs stabilize faster when you document them |
| "Nobody reads docs" | Agents do. Future engineers do. Your future self does |
| "ADRs are overhead" | A 10-min ADR prevents a 2-hour re-debate six months later |

### Red Flags

- Architectural decisions with no written rationale
- Public APIs with no documentation or types
- README that doesn't explain how to run the project
- No ADRs in a project with significant architectural choices

### Verification

After documenting:
- [ ] ADRs exist for all significant architectural decisions
- [ ] README covers quick start, commands, and architecture overview
- [ ] API functions have parameter and return type documentation
- [ ] Known gotchas are documented inline where they matter
- [ ] No commented-out code remains