Create your first CLAUDE.md (reusable skill)

Create your first CLAUDE.md

So far, you've been typing every detail into Claude Code each time you run it. That gets old fast — especially when Claude keeps making the same wrong assumptions about how you want things done.

That's what CLAUDE.md files are for. A CLAUDE.md is like a constitution for your project. It tells Claude who you are, how you work, and what rules to follow — before you even type your first instruction.

What is a CLAUDE.md file?

It's a plain text file named CLAUDE.md that you put in a project folder. When you run claude in that folder, it reads the file automatically and treats it as background context for everything it does.

Think of it as the onboarding doc you'd give a new hire. It doesn't tell them what task to do today — it tells them how things work around here.

Let's build one: Sales data project

Say you have a folder where you regularly drop sales CSVs and ask Claude to do things with them. Without a CLAUDE.md, you'd have to remind Claude every time: "use markdown tables", "format dollars with commas", "our fiscal year starts in April", etc.

Create a folder:

mkdir ~/sales-data
cd ~/sales-data

Create the CLAUDE.md file. You can use any text editor — TextEdit on Mac, Notepad on Windows, or VS Code if you have it. Save this as CLAUDE.md:

# Sales data project

This folder contains weekly sales CSV exports from Salesforce.
Files are named like sales_YYYY-MM-DD.csv.

## Context

- Our fiscal year starts April 1
- "Enterprise" deals are $50k+, "Mid-market" is $10k-$50k, everything else is "SMB"
- Revenue numbers should always include dollar signs and comma formatting
- Our sales team: Jamie, Priya, Marcus, Chen, and Aaliya

## Preferences

- Use markdown tables for any data output
- Keep reports concise — bullet points over paragraphs
- When comparing weeks, flag any rep whose revenue dropped more than 20%
- Always sort by revenue, highest first

## Rules

- Never modify the original CSV files
- Save all output files in this folder
- Use the naming convention: [type]_[date].md (e.g., report_2026-03-09.md)

Using it

Now when you drop a CSV into ~/sales-data and run claude, it already knows your fiscal year, your team, your formatting preferences, and your file naming rules. You can just say:

Summarize this week's sales.

or

Compare the last two weeks and flag anything I should worry about.

You don't have to re-explain how you want things formatted every time. The CLAUDE.md handles that.

Make it your own

The point is to capture the stuff you'd otherwise repeat. Think about:

• What does Claude keep getting wrong? Put the correction in CLAUDE.md.
• What context does Claude need that isn't obvious from the files? Write it down.
• What are your team's conventions? Document them once.

The CLAUDE.md pattern

Any project folder where you regularly use Claude Code benefits from a CLAUDE.md:

• ~/expense-reports/CLAUDE.md — knows your expense categories and approval thresholds
• ~/meeting-notes/CLAUDE.md — knows your team members and how you like action items formatted
• ~/content-calendar/CLAUDE.md — knows your brand voice and publishing schedule

One folder, one CLAUDE.md. Claude reads it every time you start a session there.

What you've learned

You now know how to install Claude Code, give it tasks, write instructions that actually work, and set up a CLAUDE.md so it remembers how you like things done. That covers the fundamentals.

Browse the automation library for more ideas, or check out the breakdowns to see how people use this day-to-day.