Boris Cherny, who built Claude Code, keeps his CLAUDE.md at around 2.5k tokens — roughly 100 lines. One developer’s was 8x that length and was getting noticeably worse results.

Here’s why it matters. CLAUDE.md loads into context at the start of every session. System prompts, tool definitions, and MCP schemas already eat 30,000–40,000 tokens before you type anything. The longer your CLAUDE.md, the less actual working context you have compared to someone keeping it lean.

Boris’s rule: add a line when Claude does something wrong, not upfront. The file grows based on real mistakes, not hypothetical ones.

Most things people put in CLAUDE.md don’t need to live there permanently. Workflows, multi-step processes, style guides — those can be skills that only load when you invoke them. CLAUDE.md should hold what needs to be true on every single request. Everything else is just overhead.