It is a design language for AI coding agents. Install it once, run one setup command, and the frontends your agent builds stop looking like every other AI frontend. Free, Apache licensed, 57,000 stars. Works in Claude Code, Cursor and Codex. Here is the problem it solves, and it is worth understanding even if you never install it. Every model was trained on the same SaaS templates. So skip the design guidance and you get the same handful of tells on every project. Inter for every heading and every body line. Purple to blue gradients. Cards nested inside cards. Grey text sitting on a coloured background. A rounded square icon tile above every heading. Once you can name those five you cannot unsee them. You will spot them on half the sites you open this week. Setup is two commands. Run npx impeccable install from your project root, then /impeccable init inside your coding tool. Init asks whether the surface is brand or product, then writes PRODUCT.md and DESIGN.md into your repo. Those two files are the actual trick. Every later command reads them, so your agent knows the audience, the voice, the colours and the anti-references without you re-explaining it on every prompt. After that you get 23 commands as shared vocabulary with your AI. polish, audit, critique, distill, animate, bolder, quieter. Instead of writing a paragraph about what feels off, you say /impeccable quieter and it knows what you mean. The part I did not expect: 59 of the checks are deterministic rules rather than model calls. The CLI and the browser extension run them with no LLM and no API key. So the audit costs nothing and gives you the same answer every time. Repo: https://github.com/pbakaus/impeccable Docs: https://impeccable.style The takeaway is not the tool though. It is that your agent produces generic design because nothing in your repo tells it who the thing is for. Write that down once and the output changes on every prompt after it.