documentation-and-adrs

---
name: documentation-and-adrs
description: Records decisions and documentation. Use when making architectural decisions, changing public APIs, shipping features, or when you need to record context that future engineers and agents will need to understand the codebase.
---

# Documentation and ADRs

## Overview

Six months from now, someone — maybe you, maybe an AI agent — will look at this code and ask "why did they do it this way?" Without documentation, that question becomes a 2-hour archaeology session
through git history, Slack threads, and deleted Jira tickets. With documentation, it's a 30-second read.

**The documentation contract:** Every significant decision gets an ADR. Every public API gets documented contracts. Every "gotcha" gets an inline comment. Code shows *what* was built; documentation
captures *why* and *what else was considered*. The future you — and every engineer who inherits your code — will thank you.

**Real-world impact:** Teams with Architecture Decision Records spend 40% less time re-debating past choices. A 10-minute ADR prevents the same architectural argument from recurring every six months.
Documentation isn't overhead — it's compound interest on your engineering decisions.

## When to Use

- Making a significant architectural decision
- Choosing between competing approaches
- Adding or changing a public API
- Shipping a feature that changes user-facing behavior
- Onboarding new team members (or agents) to the project
- When you find yourself explaining the same thing repeatedly

**When NOT to use:** Don't document obvious code. Don't add comments that restate what the code already says. Don't write docs for throwaway prototypes.

## Architecture Decision Records (ADRs)

ADRs capture the reasoning behind significant technical decisions. They're the highest-value documentation you can write.

### When to Write an ADR

- Choosing a framework, library, or major dependency
- Designing a data model or database schema
- Selecting an authentication strategy
- Deciding on an API architecture (REST vs. GraphQL vs. tRPC)
- Choosing between build tools, hosting platforms, or infrastructure
- Any decision that would be expensive to reverse

### ADR Template

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Accepted | Superseded by ADR-XXX | Deprecated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
We need a primary database for the task management application. Key requirements:
- Relational data model (users, tasks, teams with relationships)
- ACID transactions for task state changes
- Support for full-text search on task content
- Managed hosting available (for small team, limited ops capacity)

## Decision
Use PostgreSQL with Prisma ORM.

## Alternatives Considered

### MongoDB
- Pros: Flexible schema, easy to start with
- Cons: Our data is inherently relational; would need to manage relationships manually
- Rejected: Relational data in a document store leads to complex joins or data duplication

### SQLite
- Pros: Zero configuration, embedded, fast for reads
- Cons: Limited concurrent write support, no managed hosting for production
- Rejected: Not suitable for multi-user web application in production

### MySQL
- Pros: Mature, widely supported
- Cons: PostgreSQL has better JSON support, full-text search, and ecosystem tooling
- Rejected: PostgreSQL is the better fit for our feature requirements

## Consequences
- Prisma provides type-safe database access and migration management
- We can use PostgreSQL's full-text search instead of adding Elasticsearch
- Team needs PostgreSQL knowledge (standard skill, low risk)
- Hosting on managed service (Supabase, Neon, or RDS)
```

### ADR Lifecycle

```text
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

### When to Comment

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 — reset counter at window boundary,
// not on a fixed schedule, to prevent burst attacks at window edges
if (now - windowStart > WINDOW_SIZE_MS) {
  counter = 0;
  windowStart = now;
}
```

### When NOT to Comment

```typescript
// Don't comment self-explanatory code
function calculateTotal(items: CartItem[]): number {
  return items.reduce((sum, item) => sum + item.price * item.quantity, 0);
}

// Don't leave TODO comments for things you should just do now
// TODO: add error handling  ← Just add it

// Don't leave commented-out code
// const oldImplementation = () => { ... }  ← Delete it, git has history
```

### Document Known Gotchas

```typescript
/**
 * IMPORTANT: This function must be called before the first render.
 * If called after hydration, it 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 {
  // ...
}
```

## API Documentation

For public APIs (REST, GraphQL, library interfaces):

### Inline with Types (Preferred for TypeScript)

```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
 *
 * @example
 * const task = await createTask({ title: 'Buy groceries' });
 * console.log(task.id); // "task_abc123"
 */
export async function createTask(input: CreateTaskInput): Promise<Task> {
  // ...
}
```

### OpenAPI / Swagger for REST APIs

```yaml
paths:
  /api/tasks:
    post:
      summary: Create a task
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateTaskInput'
      responses:
        '201':
          description: Task created
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Task'
        '422':
          description: Validation error
```

## README Structure

Every project should have a README that covers:

```markdown
# Project Name

One-paragraph description of what this project does.

## Quick Start
1. Clone the repo
2. Install dependencies: `npm install`
3. Set up environment: `cp .env.example .env`
4. Run the dev server: `npm run dev`

## Commands
| Command | Description |
|---------|-------------|
| `npm run dev` | Start development server |
| `npm test` | Run tests |
| `npm run build` | Production build |
| `npm run lint` | Run linter |

## Architecture
Brief overview of the project structure and key design decisions.
Link to ADRs for details.

## Contributing
How to contribute, coding standards, PR process.
```

## Changelog Maintenance

For shipped features:

```markdown
# Changelog

## [1.2.0] - 2025-01-20
### Added
- Task sharing: users can share tasks with team members (#123)
- Email notifications for task assignments (#124)

### Fixed
- Duplicate tasks appearing when rapidly clicking create button (#125)

### Changed
- Task list now loads 50 items per page (was 20) for better UX (#126)
```

## Documentation for Agents

Special consideration for AI agent context:

- **CLAUDE.md / rules files** — Document project conventions so agents follow them
- **Spec files** — Keep specs updated so agents build the right thing
- **ADRs** — Help agents understand why past decisions were made (prevents re-deciding)
- **Inline gotchas** — Prevent agents from falling into known traps

## Common Rationalizations

| Rationalization | Reality |
|---|---|
| "The code is self-documenting" | Code shows what. It doesn't show why, what alternatives were rejected, or what constraints apply. |
| "We'll write docs when the API stabilizes" | APIs stabilize faster when you document them. The doc is the first test of the design. |
| "Nobody reads docs" | Agents do. Future engineers do. Your 3-months-later self does. |
| "ADRs are overhead" | A 10-minute ADR prevents a 2-hour debate about the same decision six months later. |
| "Comments get outdated" | Comments on *why* are stable. Comments on *what* get outdated — that's why you only write the former. |

## Red Flags

- ADRs written after the decision is already implemented
- Documentation that describes what the code does (code already shows that)
- ADRs with no alternatives considered ("we just picked this")
- Outdated docs that contradict the current code
- Documentation in a separate system from the code (inevitably drifts)

- Architectural decisions with no written rationale
- Public APIs with no documentation or types
- README that doesn't explain how to run the project
- Commented-out code instead of deletion
- TODO comments that have been there for weeks
- No ADRs in a project with significant architectural choices
- Documentation that restates the code instead of explaining intent

## See Also

- [spec-driven-development](skills/spec-driven-development/SKILL.md)
- [api-and-interface-design](skills/api-and-interface-design/SKILL.md)
- [shipping-and-launch](skills/shipping-and-launch/SKILL.md)

## Verification

- [ ] Every ADR links to the code it describes
- [ ] Alternatives considered section has at least 2 options
- [ ] Decision is reversible (documented how to undo if wrong)
- [ ] Documentation reviewed when code changes

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
- [ ] Rules files (CLAUDE.md etc.) are current and accurate