Context files (CLAUDE.md, AGENTS.md)

Conventions differ by tool — CLAUDE.md for Claude Code, AGENTS.md as a cross-tool convention, .cursorrules and rules files for Cursor — but the purpose is identical: give the agent the priors a new senior engineer would get on day one, so it does not re-derive them (slowly, and often wrongly) on every task.

A good one is short and load-bearing: how to run the tests, how the modules are laid out, the conventions that are non-obvious from the code, the things that look wrong but are deliberate, and the actions that need a human. A bad one is a wall of aspirational prose the agent has to wade through.

This is consistently the cheapest, highest-return item in a codebase-readiness audit. It takes hours to write, it is version-controlled alongside the code, and it improves the output of every agent and every engineer who touches the repo afterwards.