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coss ui skills Claude skills

Two skills for coss ui (Cal.com's Base UI + Tailwind v4 component library): usage rules with per-component references, and an index of 508 copy-paste particles.

cosscom/ui 2 skills Design & frontend
Our verdict Recommended with caveats

Well-sourced, official documentation for coss ui users, but useless outside that library and the particle index fetches code from coss.com at use time.

3/5 Depth expertise shipped Note Security Review before installing 1d Maintenance Updated today 11K Adoption stars ? License no clear license

What coss ui skills does

The repository is the coss ui design system itself, a monorepo of the website, docs and component registry. The agent skills live in apps/ui/skills. They teach an agent to write code against coss ui, a shadcn-style library built on Base UI and Tailwind CSS v4, instead of guessing at its API.

The first skill, coss, is a short SKILL.md (about 6 KB) backed by 62 reference files: one per primitive (dialog, menu, select, field and so on), plus notes on the CLI, the component registry and portal props. Its rules tell the agent not to invent coss APIs, to follow each primitive's documented trigger and content structure, and to use Drawer because Sheet was replaced. It also covers migrating from shadcn or Radix assumptions to Base UI. The second skill, coss-particles, is a single large index (about 44 KB) of 508 ready-made UI patterns across 54 component types, each pointing to a JSON manifest on coss.com that the agent can fetch and adapt.

It only helps if your project already uses, or is moving to, coss ui; the skills assume React, Tailwind v4 and @base-ui/react. The main repo has CI and was updated recently.

Good for

  • React projects that use or are adopting coss ui / Base UI
  • Migrating shadcn/Radix components to Base UI
  • Looking up an existing UI pattern before writing custom markup

Not for

  • Projects on other component libraries
  • Generic UI design or visual direction

What's inside depth 3/5

Two skills: a 6 KB instruction file with 62 reference files, and a 44 KB index; no scripts, tests or evals in the skill folders.

Skills
2
Reference docs
62
Scripts
0
Tests / evals
0
Templates
0
Avg SKILL.md
24.3 KB

Counted from the repository file tree. How we score depth.

Dependencies and costs

  • A React project with Tailwind CSS v4 and @base-ui/react
  • Network access to coss.com to fetch particle JSON manifests

Security review

Review before installing

Two skills for the coss UI component library: reference docs for 54 primitives and an index of 508 copy-paste 'particles' whose source the agent fetches from coss.com. Installation uses the unpinned shadcn CLI (npx shadcn@latest) to add components to your project. We hold under 5% of the repository and no code files, so only the skill Markdown was reviewed.

Worth knowing

  • Runs remote code at an unpinned versionSkill tells the agent to run npx shadcn@latest add @coss/<component> / shadcn@latest init @coss/style, executing the newest shadcn CLI and pulling registry components from coss.com into the project.apps/ui/skills/coss/SKILL.md:88
  • Makes network requestsThe particles skill has the agent fetch component source manifests from https://coss.com/ui/r/<particle>.json (508 entries) and adapt the returned code; this is code/data the agent copies into the project, not behavioral instructions.apps/ui/skills/coss-particles/SKILL.md:25
  • Installs packages or toolsSkill tells the agent to install the dependencies listed in each component's docs (React, Tailwind v4, @base-ui/react, etc.).apps/ui/skills/coss/SKILL.md:93
  • Relies on a CLI or package we could not reviewDepends on the shadcn CLI and the coss.com registry, whose code is not in the files we hold.apps/ui/skills/coss/references/cli.md:6

What we checked

The repository (3297 files) on Oct 29, 2026. Not a full review: 3129 of 3297 files were not downloaded (large repository; we reviewed the skill folders); it relies on code outside the repository: 3,129 of 3,297 repo files are not in our snapshot (the coss UI component source, registry, docs app and CI); npm package shadcn@latest and the coss.com registry JSON served at https://coss.com/ui/r/*.json.

NVIDIA SkillSpector static scan: 78 pattern hits (MCP Rug Pull 71, Excessive Agency 4, Privilege Escalation 3). Most of the 78 SkillSpector hits are npx shadcn mentions in component reference docs; the .env.local line is README setup and 'without confirmation/checking' are UI-pattern notes (e.g. confirm dialogs), not agent autonomy instructions.

A review, not a certification. Skills change after we check them — read the files before installing.

License

MIT — commercial use allowed (the README and skill frontmatter say MIT; GitHub's license detector reports it as unrecognized).

Can it run unattended?

Not really. These are reference skills for interactive UI coding; they have no loop, stop condition or verification step.

Alternatives to coss ui skills

shadcn/ui skills

shadcn-ui/ui

The official skills inside the shadcn/ui repo: a shadcn skill for adding, fixing and styling components, plus a Radix-to-Base-UI migration skill.

Recommended Check first Depth 4/5

UI Skills

ibelick/ui-skills

Nine skills for design engineers: a UI baseline checklist, accessibility/metadata/motion fixers, a design.md generator, and canvas builders for components.

Recommended Broad access Depth 2/5

Emil Kowalski's Skills

emilkowalski/skills

Sixteen design-engineering skills on animation, Apple-style motion, mobile feel, UI libraries and Swift, written by the author of Sonner.

Recommended Check first Depth 3/5

Vercel Agent Skills

vercel-labs/agent-skills

Vercel's official 9-skill pack: React and Next.js performance rules, composition patterns, UI and writing review, React Native, deploy and cost audit.

Recommended Broad access Depth 3/5

FAQ

What are the coss ui agent skills?

They are two skills inside the cosscom/ui repository: coss, which gives usage rules and per-component references, and coss-particles, which indexes 508 copy-paste UI patterns. They help an agent write correct code for the coss ui component library.

How do I install the coss skills?

The skills live under apps/ui/skills in the repo, so copy those folders into your agent's skills directory or install them with a skills CLI that supports subfolders. The skills assume your project already has Tailwind CSS v4 and @base-ui/react.

Is coss ui the same as Origin UI?

coss ui is the successor to Origin UI after Cal.com took it over. Per the README, Origin UI remains as a legacy snapshot with limited support, and active work is on the Particles components.

coss ui skills vs shadcn skills?

coss ui follows a copy-paste approach like shadcn but builds on Base UI rather than Radix. The coss skill covers migration pitfalls between the two. If you use shadcn/ui, use its own skills instead.

Sources: GitHub repository (stars, license, file tree, last push Oct 28, 2026). Review based on the README and SKILL.md files as published.