Where does the bug appear (feature/product)?
Cursor IDE
Describe the Bug
Mezmo MCP auth is working but agents on Cloud and IDE cannot list the tools from the Mezmo server. I confirmed I can curl the server directly for the list of tools but agents cannot.
Cursor’s analysis of the connection being broken due to schema changes from Mezmo and validation errors on Cursor
What’s actually happening
Cursor connects to Mezmo, fetches all 30 tools, then runs each tool’s JSON Schema through its validator. Several Mezmo tools (indices 18, 26, 29 — these line up with get_node_catalog/search_pipeline_node_schemas params, the raw_catalog output, and update_pipeline_component’s payload) use free-form/untyped object schemas that Cursor’s validator rejects as “Invalid input.” When that validation fails, Cursor drops the entire tool list and the server falls back to advertising only mcp_auth.
That’s why you see:
connected=true in the logs, but
only mcp_auth in the tool list, and
unstable CallMcpTool routing (it later idle-suspends: idle-suspending transport after 652s idle: user-mezmo).
Implication
Reloading/restarting Cursor won’t fix this — the tools will keep failing validation every time. This is a compatibility mismatch between Mezmo’s emitted tool schemas and Cursor’s schema validator. Real fixes require one side to change:
Mezmo tightening those params/payload/raw_catalog schemas (giving them proper type/property definitions), or
Cursor loosening its validator, or
a Cursor version where MCP tool validation is more permissive.
You could file this with Mezmo (their MCP server emits schemas Cursor’s client rejects) and/or Cursor support — the log excerpt above is the exact evidence they’d need.
Steps to Reproduce
Connect to MCP with a valid api key
Ask cursor “What tools are available from Mezmo MCP”
Expected Behavior
Mezmo MCP tool calls are listed and useable by agents.
Operating System
MacOS
Version Information
version is 3.12.17
For AI issues: which model did you use?
Claude Opus 4.8 High
For AI issues: add Request ID with privacy disabled
N/A
Does this stop you from using Cursor
No - Cursor works, but with this issue