Project memory: CLAUDE.md

🎯Goal. Give Claude persistent instructions for your project so you don't repeat yourself every session.

1. 1Add a CLAUDE.md file to your project root. Claude Code reads it at the start of every session. Put coding standards, the libraries you prefer (pandas, seaborn), how to run your tests, and project conventions.
2. 2Keep it lean — aim for under ~200 lines. It loads into context every session, so write essentials as facts; long procedures belong in Skills (lesson 9).
3. 3Claude also builds auto memory as it works, saving learnings like build commands and debugging insights across sessions without you writing anything.

✓You'll see. Claude following your conventions automatically — using your test command and preferred libraries without being told each time.

💳Cost. CLAUDE.md is loaded every session, so trimming it to essentials keeps your base context (and per-message cost) small.

💡Takeaway. Write the rules once in CLAUDE.md and every future session starts already knowing your project.