`MCPX_HTTP_5XX`

Severity: warn Domain: HTTP

What happened

The upstream MCP server returned a 5xx status. mcpproxy classifies this as a server-side problem rather than a misconfiguration. Common subcategories:

500 Internal Server Error — uncaught exception in the upstream.
502 Bad Gateway / 504 Gateway Timeout — load balancer in front of the MCP server lost the backend.
503 Service Unavailable — the upstream is rate-limiting or under maintenance.

How to fix

1. Check the upstream's status page

If the vendor publishes a status page, that's the fastest signal. Try again when they report the incident as resolved.

2. Retry with backoff

mcpproxy applies exponential backoff to upstream connections automatically. If the failure is transient you'll see the server flip back to Ready without intervention.

3. Look at the response body

bash

mcpproxy activity show <id>

Many upstreams put a useful diagnostic in the body even on 5xx (request id, correlation id) — quote that to upstream support.

4. Persistent 5xx on a self-hosted upstream

Check the server's own logs. The fix is on the upstream side; mcpproxy is just a faithful messenger.

MCPX_HTTP_CONN_REFUSED — connection rejected before HTTP
Activity Log

MCPX_HTTP_5XX