[Bug] MCP endpoint returns 'Service Unavailable' while service is working correctly

[IAliceBobI]

Description

When curling the MCP endpoint at http://127.0.0.1:9000/mcp, it returns Service Unavailable, but the BrowserOS MCP service is actually working correctly.

Steps to Reproduce

1. Start BrowserOS
2. Run: curl -s http://127.0.0.1:9000/mcp
3. Response: Service Unavailable

Expected Behavior

The MCP endpoint should return a proper response (e.g., MCP server info or a valid JSON response) when the service is running.

Actual Behavior

Returns Service Unavailable even though the service is fully functional.

Evidence

Despite the Service Unavailable response from curl, the MCP tools work correctly:

mcporter call browser-mcp.browser_open_tab url=http://www.baidu.com active=true
# Output: Opened new tab: Untitled
# URL: http://www.baidu.com/
# Tab ID: 1697407683

Environment

• BrowserOS version: latest
• OS: macOS

Suggested Fix

The MCP HTTP endpoint should properly respond to health check requests or provide a valid MCP response instead of returning Service Unavailable when the service is actually running.

[flhofer]

hi,
Similar issue here.

• curl http://127.0.0.1:9000/mcp returns Service Unavailable%
• curl http://127.0.0.1:9300/mcp returns Upgrade Required%
• curl http://127.0.0.1:9000/health returns {"status":"ok"}%

Does anybody have a clue? I tried using v0.39, but the results are the same.

Looking at the logs, it seems like the cdp port is not staying open. As MCP is using the cdp port, it just stops working (I didn't get it to work)

[Rvn0xsy]

Same issue with me

[shadowfax92]

Thanks for reporting! The MCP server got a big overhaul in v0.41.0. Can you try updating and let us know if this is still happening?

[IAliceBobI]

Thank you @shadowfax92 for the MCP overhaul! The MCP integration is working great now in v0.41.0. Really appreciate the quick fixes and improvements! 🚀