21st
YC W26Infrastructure and UI building blocks for the agentic internet
San Francisco, CA, USAFounded 20253 employees21st.dev
Team
3
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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Dev Tools
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