21st.dev provides the building blocks to create AI agents and agent-powered apps, including UI components, agent templates, and an SDK with built-in UI, tools, memory, observability, and managed infrastructure. The platform serves as the largest React component registry for AI applications, used by 1.4M developers with 200K monthly active users.

The SDK enables developers to define agents in TypeScript with simple syntax like agent({ model: 'claude-sonnet-4-6', tools: {...} }). It offers one-command deployment with npx @21st-agents/cli deploy, providing sandboxed cloud execution that's managed automatically. The platform includes a drop-in React UI component that's production-ready with streaming capabilities, tool execution rendering, and theming options.

The agent execution layer handles the complex infrastructure required for modern AI products, allowing developers to focus on their unique agent capabilities rather than rebuilding foundational systems. The SDK provides built-in observability features including session replay, tool call traces, and error tracking to help developers monitor and debug their AI applications.

The platform helps developers build better AI products faster by eliminating the need to create agent UI, sandbox execution infrastructure, streaming systems, and observability platforms from scratch. This allows teams to leverage advanced AI capabilities like Claude Code's reasoning, context handling, and developer workflows without building complex infrastructure.

The target users are developers building AI applications and agent-powered products, particularly those who want to integrate Claude Code-level capabilities into their applications. The platform integrates with React applications and provides full control over code while handling the underlying infrastructure automatically.