21st
A library of thousands of ready-made, AI-friendly React design components you can drop into a project — or ask your AI coding assistant to install for you.
🔗 Visit 21st
Description
Building a polished user interface from scratch is slow, and most developers end up re-solving the same problems — buttons, modals, pricing tables — that thousands of other projects have already solved well. 21st.dev is a community-built catalog of React components designed to be pasted straight into a project or installed automatically by AI coding tools like Cursor, Claude Code, or v0, so you get a professional-looking UI piece without designing or coding it from zero.
The registry holds 10,000+ components and templates compatible with the shadcn/ui ecosystem, shipped as AI-ready prompts. Beyond the component library, 21st also builds developer-facing infrastructure: Magic MCP (an MCP server integrating the registry directly into AI coding tools, 5,500+ GitHub stars) and a 21st SDK/Agent Elements for adding sandboxed, streaming AI agents with production-ready chat UI to applications. Pricing ranges from a free tier (2 component copies/day) to Builder ($6/month, unlimited copies) and Builder+AI ($15/month, plus AI credits); Team plans are $7.50/seat/month. It's a YC W26 company with users at Google, Meta, Shopify, and Vercel.
💬 Our review
The short version: if you're building UI with an AI coding assistant, 21st.dev's component registry is a genuine time-saver — instead of prompting an LLM to generate a button from scratch, you point it at a battle-tested component that's already been used and refined by thousands of other developers.
Against shadcn/ui itself (free, foundational, but a smaller base set you build up yourself) and Magic UI (also free, more animation-focused), 21st.dev's edge is scale and AI-tool integration — the Magic MCP server plugs the registry directly into Cursor/Claude Code/Windsurf so components install with a prompt rather than a copy-paste. The free tier's 2-copies-per-day cap is stingy for active use, pushing most real users to the $6/month Builder plan, which is inexpensive relative to the time saved. The newer AI agent SDK (sandboxing, streaming, billing) is a more ambitious, less proven bet compared to established options like the Vercel AI SDK, so treat that part as early-stage. For UI components alone, it's a clear win for teams already using AI coding tools; for production agent infrastructure, it's worth watching rather than betting on exclusively yet.
📊 Global score
🤖 AI-enriched data
Gratuit : 2 copies de composants/jour. Builder : $6/mois (copies illimitées). Builder + AI : $15/mois (+ crédits IA). Team : $7.50/siège/mois.
Pros
10 000+ composants prêts à l'emploi compatibles shadcn/ui
Intégration native aux outils IA via Magic MCP
Utilisé par de grandes équipes (Google, Meta, Shopify, Vercel)
Projets open-source (Magic MCP, 21st SDK)
Cons
Palier gratuit limité à 2 copies/jour
SDK d'agents IA plus récent et moins éprouvé
Meilleur tarif nécessite un engagement annuel