Today's concept: CLAUDE.md, teaching Claude your codebase
If you want Claude to stop suggesting bad ideas in your codebase, stop hoping it'll read your mind, write it a CLAUDE.md instead.
CLAUDE.md is a file you create at your repo root that tells Claude Code about your project: conventions you follow, architecture decisions, what state things are in, what to avoid, how you like to collaborate. Think of it like writing a README for the way the code works, not just what it does. When Claude Code opens your repo, it reads CLAUDE.md first, before touching any code.
In long agentic workflows where Claude makes repeated suggestions over many turns, a solid CLAUDE.md up front pays back huge token savings: Claude stops asking "should I refactor this?" or making assumptions about error handling, because it already knows your rules. Without it, you burn tokens steering Claude back on track, turn after turn. This scales poorly, the longer the agent runs, the more you pay for context you should've written once.
Quick check before you scroll: If Claude Code doesn't have a CLAUDE.md in your repo, what might go wrong?
Full breakdown + the answer: frankduah.me/learnings/2026-07-15-claude-md-teaching-claude-your-codebase
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The answer
Claude will make assumptions about your architecture, conventions, and preferences instead of knowing them. It might suggest refactors you don't want, add over-engineered error handling, miss context about why code is structured a certain way, or not know about project constraints. CLAUDE.md prevents this by front-loading the context.