23 Best 21st.dev Alternatives & Competitors

21st.dev is a community-driven React component registry built on shadcn/ui, offering Tailwind components, blocks, and hooks that install straight into a project. It works as a marketplace rather than a fixed library, with 1.4M developers and roughly 200K monthly actives pulling from the same catalog. Alongside the registry, 21st.dev ships an agent deployment SDK and an AI agent registry, and that second half of the product is what the alternatives below address. Component quality varies, since contributions come from the community rather than a maintained core team. The registry is also shadcn/ui-only, so a stack built on MUI or Chakra gets limited use out of it. Pricing for the agent SDK has not been published, which makes it hard to plan around for anything past a prototype. The 23 21st.dev alternatives below are agent frameworks and runtimes. They range from orchestration libraries like LangChain and LangGraph to multi-agent systems like CrewAI and AutoGen, typed frameworks like Pydantic AI, TypeScript-first options like Mastra and the Vercel AI SDK, and visual builders like Dify. Each one links to a full profile and a head-to-head comparison.