21st
Infrastructure and UI building blocks for the agentic internet
Operating in b2b based in San Francisco, CA, USA, 21st operates.
Profile
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.
Its activity falls under b2b; the profile below is assembled from public directory data.
Its base of operations is San Francisco, CA, USA.
Its current recorded stage is Winter 2026.
Recorded headcount: 3 employees.
Directory analysis
21st.dev is a B2B platform headquartered in San Francisco that offers a React component registry focused on AI applications. It supplies UI components, agent templates, and an SDK with built‑in UI, tools, memory, observability, and managed infrastructure, used by 2 million developers with 370 k monthly active users.
Positioning: The company positions itself as a foundational infrastructure for building agentic internet applications, targeting developers who need reusable AI components. Its sizable developer base signals traction, though its funding status and growth trajectory are not publicly disclosed.
Note: 21st.dev provides a library of React components specifically for AI agent applications.
Auto-generated directory analysis from public data · updated 8 Oct 2026. Informational only, not investment advice.
| Sector | B2B |
|---|---|
| Headquarters | San Francisco, CA, USA |
| Country | USA |
| Employees | 3 |
| Stage | Winter 2026 |
Website: 21st.dev
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