21st
YC W26Infrastructure and UI building blocks for the agentic internet
San Francisco, CA, USAFounded 20253 employees21st.dev
Founded
2025
About
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.
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