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What's a `claude.md` File? And Why It Matters in Claude-Code Projects

If you’re building with Claude-code, the claude.md file is your control panel. It’s how you set constraints, establish the project structure, and teach the AI how to operate within your stack - without bloating the codebase or relying on fragile comments. Think of it as a highly opinionated prompt that rides along with every request, telling Claude what to do, what not to touch, and how to keep the output production-ready.

It’s not generic markdown. claude.md is specific to Claude-code’s project-aware coding flow. It feeds Claude system-level instructions it uses to safely generate, edit, or refactor your codebase.

Want to try it? Here’s the Gist of my claude.md file from a real Astro + Claude-code project setup.

Optimize Carefully-This File Gets Sent with Every Claude Request

Because claude.md gets included with every interaction inside Claude-code, it’s part of your token budget. That makes it critical to keep this file lean and intentional. Too much verbosity or unnecessary commentary? You’ll slow things down, waste tokens, and risk the AI missing important directives in the noise.

Best Practices for Optimization:

  • Use short, declarative bullet points.
  • Trim redundancy—if the folder name makes it obvious, don’t re-explain it.
  • Avoid long-winded descriptions. You’re writing for Claude, not onboarding a junior dev.
  • Only include rules that Claude actually needs to know to do the work.

What’s Inside This claude.md File (Quick Rundown)

Here’s a one-liner breakdown of each section from the file I used in my Astro blog project:

  • Tech Stack - Declares framework versions and tooling: Astro, Tailwind, GSAP, TS.
  • Project Structure - Outlines directory roles like components, content, layouts, and scripts.
  • Components Rules - Sets standards for props, animation behavior, font use, and styling priorities.
  • Content Rules - Defines where blog content lives, frontmatter format, and schema validation setup.
  • Performance - Flags target Lighthouse scores, animation testing, and image optimization.
  • Commands - Lists critical npm scripts for build, preview, test, and UI testing.
  • Do Not Section - Prevents Claude from rewriting working code or skipping critical tasks like accessibility checks.
  • Quick Reference - Fast reminders for common tasks: adding posts, building components, and testing.

Astro + Claude-Code + Cloudflare = Solid, No-BS Setup

This stack works well: Astro handles the static site side - fast, clean, and easy to structure. Cloudflare Pages gives you free global hosting with quick deploys. And Claude-code picks up the slack when you need to scaffold pages, tweak components, or enforce structure without doing it all by hand. No bloated frameworks, no surprise bills - just a clean dev loop that gets out of the way.