# When an MCP connection fails, which stage failed?

MCP Connect Diagnoser: Agent tooling, Python. Repository created Oct 2026.
Code: https://github.com/jlov7/mcp-connect-diagnoser-release
Page: https://jasonlovell.ai/projects/mcp-connect-diagnoser

Checks a local MCP server stage by stage and names the one that failed.

## Design choice

Walk the session one stage at a time and keep a report for each attempt.

## In practice

A failed connection is a failed stage. Name it before changing anything.

## What I built

- Stage-by-stage session checks: initialize, ready, ping, tool discovery
- Catalogue fingerprints marked changed, unchanged or unavailable
- Every report kept, so a failure and its recovery can be compared
- Saved reports compared offline, after the server has exited

## Where it stops

Local loopback addresses only, MCP protocol versions 2025-11-25, 2025-06-18 and 2025-03-26, and at most 16 targets, 4 at a time. It does not say whether a server is safe or production-ready.

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By Jason Lovell. Independent work, separate from my role at PwC.