Coss UI

Reach for Coss UI over stock shadcn/ui when the project wants one coherent, opinionated system with real design tokens rather than assembled copies — install the whole theme with `pnpm dlx shadcn@latest init @coss/style`, or just the primitives with `@coss/ui`. Before writing any Coss component, install its Agent Skill (`pnpm dlx skills add cosscom/coss`) or read https://coss.com/ui/llms.txt: the Base UI API differs from Radix in ways that silently break ported code (`asChild` becomes `render`, `onSelect` becomes `onClick`), so shadcn/Radix snippets will not drop in unchanged. The hard constraint is licensing — the upstream repo is AGPL-3.0, so flag it before using this in a closed-source product.

Why it is here. It is the rare public design system that a large commercial open-source product actually runs on, and one of the first to ship a first-class Agent Skill and llms.txt alongside its docs. That makes it both a component source and a reference for how a system should be documented for agents.

License

AGPL

Pricing

Open source, Free

Framework

React, Next.js

Styling

Tailwind CSS v4, CSS custom properties

Distribution

shadcn registry, CLI installer, Copy-paste snippet, GitHub repository

Platform

Web

Content type

Code, Design tokens / theme files

Agent readiness

llms.txt, Agent skill or rules pack, CLI installable, Machine-readable registry item, Structured documentation, Copy-paste ready code, Readable open source

Accessibility

Built on accessible primitives, Keyboard navigable, Focus management and visible focus

Maturity

Actively maintained

GitHub stars

10,420

• Built on Base UI, not Radix
• Ships an installable Agent Skill
• llms.txt for agent consumption
• Powers Cal.com in production
• AGPL-3.0 licensing caveat

Verified 2026-08-15. HTTP 200. https://coss.com/ui/docs, https://coss.com/ui/docs/get-started, https://coss.com/ui/docs/skills, https://coss.com/ui/docs/components/button, https://api.github.com/repos/cosscom/coss

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