21st

Introducing @21st_dev Agent Elements Diffed edits. Plan approvals. Clarifying questions. Sub-agents. Tool cards. The pieces every "agent UI" lib skips. 25 @shadcn /ui components built for the new generation of agents that use your computer. Open-source. Link in thread 🧵

built a Lottie animation generator agent on @21st_dev SDK. → prompt → valid Bodymovin JSON (shape layers, keyframed transforms, bezier paths) → live preview + scrubbable timeline with hover-scrub → copy json or one-click download → thinking banner with live phase hints while the agent writes 100% open-source. you can run it in 60 seconds 🧵

built a SQL agent UI with @21st_dev SDK — chat to query OR mutate a live table grid — read/write toggle sits right in the chat input — new rows pulse green when the agent INSERTs — the active tab follows whatever the agent touches under 500 LOC, full template ↓

Generate websites with OpenClaw 🦞 Add the @21st_dev MCP in @atomicbot_ai Your agent runs the flow: → Generates UI variants → Picks the best result → Ships it into your desktop project Open-source. Local models supported.

Introducing Agent Registry for Anthropic Managed Agents

1,030 people used 21st.dev in the last 30 minutes. If you’re one of them, say hi in the comments 👋

Your docs agent should not stop at “not found in docs.” So I turned our docs template into a simple support agent. If the docs cannot answer, the agent forwards the question to your team by email. Built with Claude Code + 21st SDK + @resend Takes just a few minutes to add. Demo below 👇

Stop sending users to a docs tab. Let them chat with docs inside your product. - Built with Claude Code + @21st_dev SDK - Works especially well with @mintlify - Setup takes ~2 minutes. Demo below 👇

We had no idea when engineers from OpenAI or Stripe signed up. So we built a lead research agent. Claude Code + @ExaAILabs researches each signup by email and pings Slack when someone interesting appears. Template on 21st 👇

Let your agent set everything up for you

Big update: 21st SDK x @OpenRouter 🤝 Now you can keep runtime: "claude-code" and run your agents on OpenAI / Gemeni models via OpenRouter model IDs. Same Claude Code-style workflow. More model choice. 🧵

21st was just named one of the top DevTech startups in W26 by The Silicon Valley Post

The official 21st SDK for Go is here! Manage AI agent sandboxes, threads, and tokens — straight from your Go backend. Here’s how to get started 🧵

@21st_dev × @agentmail New template to build Claude-powered agents with real email access - out of the box.

Nia now integrates with @21st_dev (YC W26): chat with any GitHub repo using 21st Agents SDK. Index a repo, spin up a sandboxed agent, and get answers grounded in the full codebase.

Someone made a YC W26 tier list. 21st ended up in S tier. Appreciate the vote of confidence. Back to building.

🎉 New Investment: @21st_dev 🎉 Excited to share that I’m investing in 21st alongside @YCombinator. 21st is building infrastructure and UI building blocks for the agentic internet. Their platform is already used by over a million developers building AI-native products, providing reusable components, templates, and tooling specifically designed for AI applications and agents. Their newest product, the 21st Agents SDK, makes it dramatically easier for developers to embed production-ready AI agents directly into their applications. Instead of building complex infrastructure from scratch, developers can define an agent in a few lines of TypeScript and deploy it instantly. The SDK includes built-in chat UI, sandboxed execution environments, tool integration, streaming responses, cost tracking, and observability — all the infrastructure required to run real AI agents in production. One exciting use case is integrating Claude Code–powered agents directly into products. With the 21st Agents SDK, teams can quickly add powerful agent capabilities to their apps without building the underlying agent runtime themselves, enabling a new generation of AI-native software. The company is founded by @serafimcloud and @sergeybunas, two builders deeply embedded in the developer ecosystem. Serafim previously built widely used developer products and crypto infrastructure, while Sergey built UI systems at Deel and has repeatedly launched developer tools that gained strong early traction. Their product taste and speed are clear in what they’ve already shipped. Excited to support them as they build core infrastructure for the next wave of AI applications.

We're launching 21st Agents in beta. It's the infrastructure layer for Claude Agent SDK - runtime, sandboxing, billing, UI, streaming - so you can ship agents to production without building infra from scratch. Think Vercel for Claude Agent SDK. Full walkthrough in the video below 👇

21st Agents SDK is live on Product Hunt 🔥🔥 producthunt.com/posts/21st-age…

We’re building Next.js for frontier agents!