guide
What is DESIGN.md? (and AGENTS.md, CLAUDE.md, llms.txt)
DESIGN.md is a plain-text file that describes a brand's design system (colors, typography, spacing, components and rules) so that people and AI tools build from the same decisions. It lives in a project or is attached to a chat, and AI tools read it as context before they write or design.
The files you will meet
| File | What it is | Who reads it |
|---|---|---|
DESIGN.md | The full design system in markdown. brandmarkdown follows the format published by Google Labs (github.com/google-labs-code/design.md): tokens in a header block, rules in the body. | People, Claude, ChatGPT, Cursor, v0, Lovable |
AGENTS.md | Instructions for coding agents working in a repository. | Codex, Jules, Aider and other agents that read AGENTS.md |
CLAUDE.md | Project memory that Claude Code loads in every session in that folder. | Claude Code |
.cursor/rules/*.mdc | Rules Cursor applies to matching files. | Cursor |
llms.txt | A short index at your website root that points AI search and agents to your key pages. | AI search, agents |
Why markdown
A brand book PDF is written for people and is hard for a model to use. Markdown is plain text with headings and tables: a model reads it exactly, and you can keep it in the same place as your website or your prompts.
See a complete example: the DESIGN.md of a sample brand.