Kumo

Why it's ranked here

What sets this apart from the average component library is the generated metadata: props, variant values and demo code are derived from the TypeScript source and published for agents to read, and the same data answers a terminal query. That is a real reason to pick it if you want a model writing consistent UI code. The cost is coupling. Cloudflare branding components are first-class exports, one theme targets FedRAMP, the package is ESM only, and the workspace pins a recent Node major. Fine inside a Cloudflare-shaped stack, awkward as a neutral house style.

What's good

Supply chain hygiene is unusual and welcome: the workspace refuses to install any dependency published in the last three days, with a short explicit exclusion list. Token discipline is enforced by five custom lint rules rather than a style guide nobody reads, so raw color classes and dark variants fail the check. Imports are per component, so you can pull one widget without the rest. Base UI primitives are re-exported for cases where the styled wrapper is too opinionated. Contributions require a changeset, validated by a pre-push hook.

Tradeoffs

The toolchain is all-in on one vendor: build, test, lint and format run through a single unified CLI, so contributing means adopting it rather than your usual setup. ESM only, no CommonJS build. A specific icon package is a required peer dependency. Two exported components are already marked deprecated in the entry module, which suggests the API is still moving. Blocks are copied into your repository rather than imported, so you own their maintenance after install. Generated registry files are absent from the tree; they arrive at build time and in the published package.

How to use it well

Best fit: a team building an internal console or admin UI in React that wants accessibility handled and is happy to inherit someone else's token names. It earns a slot when agents write your components, because the terminal documentation command and the shipped metadata give the model an exact prop surface instead of guesswork. It does not cover routing, data fetching or form state, and it is not a white-label system: the logo components and default palette are Cloudflare's. Bring your own icons, since one icon package is required.

Observed

License

MIT, Cloudflare, Inc. (LICENSE)

Language

TypeScript and React, ESM only, no CommonJS build

Install surface

npm package @cloudflare/kumo, plus subpath imports per component and per primitive

Interfaces

React library and an npx CLI: init, blocks, add, ls, doc, docs, migrate, ai

Peer dependencies

react, react-dom, @phosphor-icons/react

Repository shape

pnpm monorepo: component library, Astro docs site, Figma plugin, screenshot worker

Supply chain policy

pnpm-workspace.yaml rejects dependencies published within the last three days, with a named exclusion list

Lint rules

lint/kumo-plugin.js registers five custom oxlint rules covering color tokens, dark variants, variant shape, cross-package imports and flow rendering

Accessibility base

Built on Base UI, whose primitives are re-exported

Agent surface

Component registry generated from TypeScript types, queryable from the CLI and shipped in the package