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.
| # | Tool | Best for | Price |
|---|---|---|---|
| 1 | Design engineers et développeurs front-end qui construisent des sites web/apps avec React, TypeScript et Tailwind CSS | — | |
| 2 | Développeurs | — | |
| 3 | Développeurs | — | |
| 4 | Développeurs web construisant une interface de chat IA ou un widget d'assistant sur leur site | — | |
| 5 | Développeurs React utilisant React Router et voulant des transitions de page animées sans les coder à la main | — | |
| 6 | Développeurs TypeScript/JavaScript ayant besoin de gérer proprement les échecs réseau ou d'appels externes | — | |
| 7 | Développeurs et équipes construisant des apps web/mobile qui veulent une API REST gérée sans écrire de backend | — | |
| 8 | Développeurs Python (3.13+) construisant des applications web, en particulier les équipes qui utilisent des agents IA de codage et veulent du code explicite et typé | — | |
| 9 | Développeurs et propriétaires de blogs/sites de documentation hébergés sur GitHub cherchant des commentaires légers sans base de données | — | |
| 10 | Développeurs et petites équipes voulant un constructeur de site visuel sans les frais mensuels de Webflow ni la lourdeur de WordPress | — | |
| 11 | Développeurs qui construisent des SaaS, outils BI, applications IA ou outils internes ayant besoin d'édition de tableurs/documents/présentations intégrée | — | |
| 12 | Créateurs, marketeurs, petites entreprises, consultants, freelances et coachs voulant un site web sans designer | — |
A free library of pre-built, animated building blocks for websites — instead of a developer hand-coding a fade-in effect or a particle background from scratch, they copy a ready-made component into their project and adjust it, the same way people already
A free, open-source code library that lets developers add an AI chat assistant to their website without relying on any particular framework.
Adds smooth, movie-like transitions between pages in a React app — instead of the page just snapping instantly to the next screen.
A small toolkit that adds retry, timeout, and fallback behavior to any function that can fail — like a network call — so a flaky API doesn't crash your whole app.
A tool that builds a working, ready-to-use API for your app just by describing your data, so you can skip writing backend code and connect your website or app straight to a database.
A Python web framework that grew out of a real company's Django app, built explicitly so AI coding assistants (and humans) can understand and safely modify the code.
A free comment box you can drop into any blog or website, that stores every comment as a normal GitHub Discussion instead of a database you have to maintain.
A free, self-hosted website builder with a visual page editor, like Webflow or WordPress, but one you run on your own server instead of paying a monthly fee to a company.
