Skip to main content

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​

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.