Base UI

Choose Base UI over Radix when the design calls for a Combobox, Autocomplete, Drawer, OTP Field or Field-level validation wiring, since Radix has no first-party equivalent and you would otherwise bolt on cmdk plus Vaul plus a form library. It has the best agent-facing docs of any primitive library here: fetch https://base-ui.com/llms.txt, and note that the docs explicitly tell you to downgrade the Tailwind v4 examples if the project is on v3. shadcn/ui ships a Base UI variant, so check which primitive layer a project already vendors before mixing the two — running Radix and Base UI side by side duplicates portal and focus-management logic.

Why it is here. The most credible successor to Radix Primitives, built by the same people who wrote the original, and the first primitive library designed with LLM consumers in mind.