Inspector times out when FastMCP tool emits ctx.info/ctx.report_progress (v2.2.0, LEGACY/STDIO)

[Avi-Jadhav03]

Which version line?

v2 — current (@modelcontextprotocol/inspector@latest)

Which client?

Web

Inspector version

2.2.0

Node version

v26.5.0

Operating system (and browser, for the web client)

MacOS 26.5.2

Transport

stdio

MCP server under inspection

Server: FastMCP local Python server (server.py)

Command used:
fastmcp dev inspector server.py

Transport: stdio
Protocol era: legacy
OAuth: no

Note: Same server/code works via Claude Desktop; timeout is observed via Inspector path.

Steps to reproduce

1. Fresh launch Inspector using fastmcp dev inspector server.py.
2. Connect to the local server over stdio.
3. Open the Tools tab.
4. Run slow_task (example input: steps=5) where the tool calls ctx.report_progress(...) and ctx.info(...) in a loop.
5. Observe progress/log lines appear during execution.
6. Final result does not return; Inspector shows Tool Error: Request timed out.

Expected behavior

Tool should complete and return its final result in Inspector UI, while still allowing mid-execution context notifications (ctx.report_progress(...) / ctx.info(...)).

Actual behavior

When ctx.report_progress() or ctx.info() is invoked, Inspector eventually shows Tool Error: Request timed out, even though server-side execution appears to finish successfully.

If Context is injected but unused (or no Context calls are made), the tool returns normally.

Logs, errors, or screenshots

Error shown in Inspector UI:
Tool Error: Request timed out

Environment:

• Inspector version: 2.2.0
• Node.js: v26.5.0
• OS: macOS 26.5.2
• Transport: stdio
• Era: legacy

I can provide additional Protocol/Network logs if maintainers want specific traces.

Already prototyped a fix?

No fix prototyped yet.

Before you submit

• I searched existing issues and this is not a duplicate.
• This is not a security vulnerability report (those go through the private advisory process).

[carter-smalls]

Looks like tool error request timed out when ctx.report_progress is called.

Use badgr-mcp-doctor to diagnostic report showing mcp timeout cause and guidance to resolve it.

That should help confirm frequency of ctx.report_progress messages causing timeout.

[Avi-Jadhav03]

Thanks — I installed and checked badgr-mcp-doctor usage.

Its required mode is --url <sse-url> (SSE endpoint), but my repro is on stdio transport in Inspector (legacy era), not SSE.

badgr-mcp-doctor --help output indicates URL/SSE-based diagnostics only.
Could you share the exact command/flags you want for a stdio-based repro, or should I reproduce this against an SSE endpoint and report that result instead?