What is a CLAUDE.md file?

A context file that Claude reads at startup and that sets your tone, your rules, and your pitfalls. Immediate effect: you stop repeating the same instructions, and responses match your way of working from the very first message.

What goes in a CLAUDE.md?

Four families: tone & format (how formal, prose or lists, length); your conventions (industry, tools, in-house vocabulary); what you DON'T want (empty jargon, unsolicited 14-step plans, flattery); and your pitfalls, meaning mistakes you've already encountered turned into rules — the most valuable part.

What are the best practices for a CLAUDE.md?

Short beats exhaustive; concrete beats abstract (give ready-to-use commands rather than 'be helpful'); one rule = one real mistake, not speculation; and split by context (a shared base + extensions for strategy / technical).

How do you make your CLAUDE.md grow?

When Claude makes the same mistake repeatedly, add the rule. The file improves with use — that's the Compound Engineering principle applied to your context.

Writing a good CLAUDE.md (the most valuable file you'll ever create)

1. Why it's the best investment

Without a CLAUDE.md, you re-brief Claude at the start of every conversation: "answer in English, get to the point, here's my job…". With one, it's set once and for all. The return on the time invested is immediate — it's the first thing I recommend to anyone just getting started.

2. What goes in it

Four families of things:

Tone & format: formal or casual, prose or lists, short or detailed.
Your conventions: your industry, your tools, your in-house vocabulary.
What you do NOT want: empty jargon, unsolicited 14-step plans, flattery…
Your pitfalls: mistakes you've already encountered, turned into rules. This is the most valuable part.

Tone & formatHow formal, prose or lists, response length.

ConventionsIndustry, tools, in-house vocabulary.

Off-limitsEmpty jargon, unsolicited plans, flattery.

Pitfalls → rulesMistakes you've encountered, engraved as rules. The most valuable part.

The typical structure — from most general (tone) to most valuable (pitfalls turned into rules).

3. Best practices

Short beats exhaustive. A file nobody reads does nothing.
Concrete beats abstract. "Give ready-to-paste commands" beats "be helpful".
One rule = one real mistake. Don't add speculative rules "just in case".
Split by context. Rather than one monolithic block, a shared base + extensions (e.g. one for strategy, one for technical).

4. How to make it grow

When Claude makes the same mistake repeatedly, don't just grumble — add the rule. The file improves with use. That's exactly the Compound Engineering principle applied to your context.

Before

Re-brief every time

"Answer in English"
"Here's my job…"
Same mistakes coming back

After

One CLAUDE.md

Set once and for all
Matches your style from message one
Grows from every corrected pitfall

The time saving: stop re-explaining, and quality goes up from the first message.