What actually belongs in your CLAUDE.md
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CLAUDE.md is the instruction core Claude Code reads before it does anything. Most people leave it near-empty and wonder why the output feels generic. A real one changes everything.
The sections that matter
- Who you are and how you work. Stack, conventions, the way you like code written. Claude stops guessing your preferences on every task.
- Hard rules. The things that must never happen (secrets in code, skipping tests, touching prod). Written as blockers, not suggestions.
- Verification. What "done" means for you, so Claude checks its own work before claiming success.
- Voice. How writing and comments should sound, so nothing reads like it came from a template.
The mistake almost everyone makes
Treating CLAUDE.md as a one-time file. It should grow. Every time you correct Claude, that correction belongs in the file so it never happens twice. That compounding is where the real speed comes from.
Skip the blank page
Building a strong CLAUDE.md from scratch takes weeks of trial and error. The Blubber Starter Kit ships a proven one that starts with a short interview and rewrites itself around how you actually build. Or start from the free open-source version on GitHub and grow your own.