Appendix FFor builders
Set the context
Coding agents read a project instructions file before they start. Keep it short and true: what the project is, how to build and test it, and the rules.
Claude Code reads its CLAUDE.md files “at the start of every session,”1 and OpenAI’s Codex “reads AGENTS.md files before doing any work.”2 Whatever the file is called, it goes on the desk (Chapter 2) every time, so every line costs room. As of October 2026 Spot it today: look in a project for the instructions file its coding agent reads; whatever it's called, it plays this role.
What to put in it
- What it is and who it’s for, in two lines.
- How to build, run and test it: the exact commands.
- The conventions: naming, style, where things live.
- What never to do: touch secrets, push to production, delete data.
- Where to look for more: point to longer documents instead of pasting them in.
Notes (2)
- 1Anthropic, “How Claude remembers your project,” Claude Code Docs, n.d., https://code.claude.com/docs/en/memory (accessed October 27, 2026).
- 2OpenAI, “Custom instructions with AGENTS.md,” Codex documentation, n.d., https://learn.chatgpt.com/docs/agent-configuration/agents-md (accessed October 27, 2026).
Appendix F · page 1 of 3
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