What is CLAUDE.md?

What it is: A plain-text file that sits at the top of an AI project folder. Before your AI starts any work session, it reads this file to understand how you want things done.
Who it’s for: Anyone using an AI coding assistant — like Claude Code — on a project that lasts more than one conversation.
Best if: You want the AI to stay consistent across sessions, remember your tone, and know which files are off-limits.
Skip if: You’re only using AI for one-off questions that don’t need any continuity.

Every AI conversation starts fresh. The moment you close the window, the AI forgets what you discussed. CLAUDE.md solves that problem.

It’s a simple text file — no special format required, just plain sentences — that lives at the top of your project folder. When Claude Code starts a new work session, the first thing it does is read this file. Think of it as a staff handbook your apprentice reads every morning before picking up any tools.

Inside a CLAUDE.md file you might put:

• Voice rules — “Always write at a seventh-grade reading level. Avoid jargon.”
• Off-limits files — “Never edit the homepage or the pricing page without explicit approval.”
• Conventions — “Always check whether a glossary entry exists before linking to one.”
• Scope boundaries — “This project is for blog posts only. Don’t touch the plugin folder.”

The key constraint: keep it short. A CLAUDE.md file that runs to five hundred lines is a file the AI partially skims. Most practitioners aim for under two hundred lines — enough to set the important rules, not so much that the important ones get buried.

Without a CLAUDE.md, every new session starts from zero. With one, the AI picks up in the right posture every time — same voice, same rules, same guardrails.

Related

• What is Claude Code?
• What are Hooks? (in Claude Code)