Appica UI

Pick this over shadcn/ui when you want a real npm dependency instead of copied source, and when the project already sits on Base UI rather than Radix — the two do not share primitives, so mixing them means shipping both. Its agent story is the best part: fetch https://appica.dev/llms.txt for the component index, then append .md to any docs URL for ~8KB of clean markdown per component, and read node_modules/@appica/ui-react/agent-rules.md for the version-matched ruleset before writing imports. Watch two hard constraints: React 19 (it uses ref-as-prop) and a working Tailwind v4 setup, plus the required @source directive in the global stylesheet or every utility class gets tree-shaken away.

Why it is here. One of the few 2026 libraries designed for agent consumption from the start — llms.txt, per-page markdown, and a shipped agent-rules file — rather than a docs site an agent has to scrape.