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The MCP server URL is discovered out-of-band. For Paperzilla, that usually means your client or user starts with the documented endpoint from the docs, app setup instructions, or docs indexed via llms.txt: https://paperzilla.ai/api/mcp This URL does not come from OpenAPI.

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What happens after the client knows the URL

Once the client is pointed at the MCP endpoint and has a valid MCP API key, it can discover the callable surface from MCP itself. In practice, the client initializes the MCP connection first, then calls:
  1. tools/list
  2. Optionally prompts/list
tools/list returns the available tool names plus input schemas, so the client can see what calls exist and what arguments they take. That means MCP is self-describing after connection.

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Does MCP have its own endpoints?

Externally, no per-tool endpoints are required. Paperzilla exposes one MCP endpoint at /api/mcp, and tool calls happen over that protocol connection. Internally, those tools are backed by Paperzilla’s own app logic and data access. A tool may read directly from internal services or data stores instead of calling the public REST API.

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How this relates to OpenAPI

OpenAPI documents a REST API. MCP tool discovery works differently:
  • OpenAPI tells a REST client which HTTP routes exist
  • MCP tells an MCP client which tools exist through tools/list
So if you are building an MCP client for Paperzilla, you usually need:
  • The MCP server URL
  • An MCP API key
  • Standard MCP calls like initialize and tools/list
Use OpenAPI only for Paperzilla’s normal REST endpoints, not for MCP tool discovery. See also: