#4848th of 52 in MCP servers for developers
ext-apps
SDK for rendering interactive MCP tool UIs inline in chat clients
- Stars
- 3k
- License
- custom license
- Last commit
- Sep 2026
- Last release
- Sep 2026
- Language
- TypeScript
1,934 on 31 Mar 20262,990 on 20 Oct 2026
From GitHub's daily star counts.
Checked on GitHub.
Overview
TypeScript SDK and spec for the MCP Apps extension, where an MCP tool declares a ui:// HTML resource that the host renders in a sandboxed iframe. Packages cover building Views (with React hooks), embedding them in a host, and registering UI tools on a server. The repo also ships about 20 example servers, starter templates for six frameworks, and four Agent Skills.
Who it is for: MCP server authors adding interactive UIs, and chat client developers
Strengths
- Four npm entry points cover View, React hooks, host app-bridge and server helpers
- Starter templates for React, Vue, Svelte, Preact, Solid and vanilla JS
- Example servers (map, PDF, Three.js, QR) run via npx with --stdio
- Wire protocol unchanged between ext-apps 1.x and 2.x
Weaknesses
- No supported host implementation; only the basic-host example is included
- Host support varies, since it is an extension to core MCP
- Requires Node.js 20+, MCP SDK 2.x peer packages and zod 4
- License detected as NOASSERTION, while the README badge says Apache 2.0
What it needs
- no GPU
- Needs Node.js 20+, @modelcontextprotocol/client ^2.0.0, zod ^4.2.0
- port 8080
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