A2ui MCP

Connecting to the A2UI MCP server

The default: no credential at all

https://a2uicatalog.ai/mcp

Public, unauthenticated, no signup, no API key. POST speaks JSON-RPC 2.0 (MCP Streamable HTTP): initialize → tools/list → tools/call. GET the same URL with Accept: application/json for a machine-readable server descriptor (every tool, current rate limits, docs links) instead of the human landing page.

POST https://a2uicatalog.ai/mcp
Content-Type: application/json

{"jsonrpc": "2.0", "id": 1, "method": "tools/list"}

If a scanner, spec, or setup wizard told you to look for /auth.md, this is the short answer: just call the endpoint above. The rest of this skill is about the optional authenticated path most integrations don't need.

A separate documentation server

https://a2uicatalog.ai/mcp-docs is a DIFFERENT MCP identity (a2uicatalog-docs) exposing search_docs(query) / list_docs() — it answers questions FROM this product's own docs (auth, versioning, pricing, rate limits). The server above TAKES ACTIONS (compose, render, publish); this one only answers doc questions. Don't confuse the two when an agent needs to look something up rather than do something.

Rendering inline: MCP Apps

Hosts that negotiate the io.modelcontextprotocol/ui extension in their initialize request get inline rendering: render_surface returns a live, interactive view inside the conversation via a ui:// resource — no URL, no size ceiling, nothing stored. On a host that doesn't support MCP Apps, the same tool call just returns the payload as text instead of erroring, so it's always safe to call.

When you actually need a credential

Enterprise platforms whose connector model can't call an unauthenticated service (e.g. Gemini Enterprise's BYO-MCP data store, which requires OAuth 2.0) use a second, gated endpoint: https://a2uicatalog.ai/mcp-auth — the SAME tools as /mcp, behind a real credential. Three accepted mechanisms, in precedence order: Authorization: Bearer <token> (OAuth 2.0 authorization-code flow), X-Api-Key: <key> (for connector templates that offer an API-key field but no OAuth), Authorization: Basic <base64(user:pass)>. An unauthenticated request to /mcp-auth returns 401 with a WWW-Authenticate header carrying a resource_metadata pointer to the RFC 9728 protected-resource metadata document.

There is no self-service registration — this server doesn't implement RFC 7591 dynamic client registration. Registration is manual, one client_id per organization (the client IS the tenant): contact the maintainer via https://a2uicatalog.ai/contact/ with your exact redirect_uri values. If you don't want to wait, use the public /mcp endpoint instead — it's the same server, same tools.

Machine-readable discovery documents

Free, MIT licensed, no signup for the default path. Independent, unofficial project — not affiliated with, endorsed by, or sponsored by Google or Anthropic. A2UI is Google's protocol; MCP is Anthropic's. Source: https://github.com/a2uicatalog/a2ui