automatic-documentation

name	automatic-documentation
description	Principles for writing READMEs, API docs, ADRs, code comments, and changelogs. Use when creating or improving any technical documentation.
authors	["Automatic"]

Technical Documentation

Documentation is a product. It requires the same deliberateness as code. Outdated, incomplete, or misleading documentation is worse than none — it wastes time and creates false confidence.

Principles

Write for the reader, not the writer. The author already knows how the system works. Documentation exists to transfer that understanding to someone who does not. Every sentence should serve that goal.

Document decisions, not just descriptions. Code describes what the system does. Documentation should explain why it does it that way. The most valuable documentation captures constraints, trade-offs, and rejected alternatives.

Treat documentation as a deliverable. A feature is not complete until it is documented. Documentation that is written later rarely gets written.

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Types of Documentation

README

The entry point for any project. Must answer:

• What does this project do?
• How do I get it running locally?
• How do I run the tests?
• Where do I go for more information?

Keep it short. Link to deeper documentation. It should take under 5 minutes to read.

API documentation

Document every public interface: functions, REST endpoints, event schemas.

For each item, include:

• Purpose — what it does in one sentence
• Parameters / fields — name, type, whether required, valid values or range, default
• Return value / response — what is returned and under what conditions
• Errors — what error conditions can occur and what they mean
• Example — a concrete, working example

Architecture decision records (ADRs)

Record significant technical decisions as short, dated documents:

# ADR-042: Use PostgreSQL for primary data store

**Status**: Accepted  
**Date**: 2025-03-02

## Context
We needed a relational database that supports ...

## Decision
We will use PostgreSQL 16 because ...

## Consequences
- We gain: JSONB support, strong ACID guarantees, mature tooling
- We accept: operational complexity vs. a managed service
- We reject: MySQL (weaker JSON support), SQLite (no concurrent writes)

ADRs are permanent. Even superseded decisions should be marked "Superseded" and kept — the reasoning matters.

Code comments

Comment why, not what. The code says what is happening; comments explain why it happens that way.

// Good: "Skip validation here — this path is only reachable from the
//        internal job queue, which has already validated the payload."

// Bad: "Skip validation"
// Bad: "Call the validate function" (the next line says that)

Comment anything surprising, non-obvious, or that required a decision that is not evident from the code itself.

Changelogs

Record what changed for users, not for developers.

• Group by release version and date
• Categorise: Added, Changed, Deprecated, Removed, Fixed, Security
• Link to issues or PRs for context
• Never use "Various bug fixes" — be specific about what was fixed

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Writing Style

Use plain English. Avoid jargon where a simpler word exists. If jargon is necessary, define it on first use.

Short sentences. Break long sentences into two. If a sentence requires re-reading, rewrite it.

Active voice. "The server validates the token" not "The token is validated by the server."

Present tense. "Returns the user object" not "Will return the user object."

Examples are mandatory. Abstract descriptions without examples make readers do extra work. Show, then tell.

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Maintenance

• Documentation lives alongside the code it describes — in the same repository
• Documentation changes are part of the same PR as the code changes
• Broken documentation is a bug — file it and fix it
• Deprecate documented features explicitly; do not silently remove documentation