document

name	document
description	Capture hard-won engineering knowledge in durable project documentation.
disable-model-invocation	true
argument-hint	[what to document]

Document

Capture knowledge for humans. Not for AI, not for ceremony — for the person who maintains this code in six months.

When to Use

• After completing a feature with non-obvious behavior
• After resolving a complex debugging session
• When the user asks to document something

What to Document and Where

Feature Documentation

If the project has a docs/ folder, use it. The spec file from brainstorm is a starting point, but it needs rewriting — specs are instructions for an agent, docs are explanations for a person.

Write for someone who will use or maintain this feature. What does it do, how does it work, what should they know.

Debugging Knowledge / Gotchas

When a complex issue is resolved, especially one that took significant investigation:

• What the problem was and how it manifests
• Why it happens (root cause)
• What the fix is and why it works
• What was already tried and why it didn't work
• Sources consulted (URLs, GitHub issues, docs pages)

Place this close to the relevant code: inline comments for small gotchas, a dedicated doc for complex ones.

"We Already Tried This" Notes

For complex ongoing work — like replicating engine-specific rendering in WebGL, or fighting a particularly tricky integration — maintain a living doc of approaches tried:

## Approaches Tried
- **Gamma correction swap (sRGB -> linear)** — didn't work because [reason]. See [source].
- **Manual tone mapping curve** — partially worked but [limitation].
- **[What actually worked]** — works because [explanation]. Key insight: [the non-obvious thing].

This prevents future sessions from re-treading the same ground. If the agent's first instinct is "maybe it's the gamma correction" but that was already tried and documented — the doc catches it.

Architecture Decisions

When a non-obvious choice is made, document why. Not a formal ADR — just a brief note:

• What was decided
• What the alternatives were
• Why this one was chosen

Lives in docs/ or as a comment near the relevant code, depending on scope.

Principles

• Write for the person who joins in 6 months. They don't have your session context. They don't know what you tried.
• Use the project's existing docs folder and conventions. Don't invent a new structure.
• Inline comments for small things, dedicated docs for complex ones. A one-liner "this must be called before X because Y" belongs in code. A multi-paragraph rendering pipeline explanation belongs in a doc file.
• Link to sources. If the fix came from a GitHub issue, a docs page, or a forum post — include the URL.
• Keep it current. If you're updating code that has associated docs, update the docs too.
• Don't write documentation for the sake of documentation. If the code is self-explanatory and there are no gotchas, there's nothing to document.