21st
Infrastructure and UI building blocks for the agentic internet
What 21st does
21st.dev is the largest React component registry for AI applications, used by 2M developers (370K MAU). We provide the building blocks to create AI agents and agent-powered apps: UI components, agent templates, and an SDK with built-in UI, tools, memory, observability, and managed infrastructure.
Check the company’s own careers page — linked at the top — before a job board. A role appears there first, sometimes weeks before it is syndicated anywhere else.
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Company facts compiled from public sources and last refreshed 9 September 2026. Details change; treat the company’s own site as the authority.