Claude Desktop: MCP tool calls shown in UI but never sent to server
Status Fixed / completed
Maintainer reply None cached
Workaround ✓ Mentioned in description ↑
Activity 9 comments · opened Feb 1, 2026 · closed Feb 3, 2026
Description
Claude Desktop shows tool calls in the UI (spinner appears) but the tools/call JSON-RPC message is never sent to the MCP server. The server initializes correctly and responds to tools/list, but tool calls never arrive.
Environment
- macOS Darwin 25.2.0
- Claude Desktop (latest as of Jan 31, 2026)
- Custom Python MCP server using
mcpSDK v1.26.0
Steps to Reproduce
- Configure a custom Python MCP server in
claude_desktop_config.json - Restart Claude Desktop - server initializes successfully
- Ask Claude to use one of the server's tools
- UI shows the tool being called (spinner appears)
- Tool call never reaches the server
Evidence from Logs
Server initializes and lists tools successfully:
[mcp-gmail] Module starting...
[mcp-gmail] stdio_server connected, running server...
[mcp-gmail] list_tools called
Message from server: {"jsonrpc":"2.0","id":1,"result":{"tools":[...]}}But no tools/call message ever appears in logs. Another MCP server (projects, similar Python setup) DOES receive tool calls correctly.
Workaround
Running the same MCP server code directly via CLI works perfectly - the issue is specific to Claude Desktop's tool call routing.
Additional Context
- Tried multiple config formats (module vs direct script)
- Tried with only the affected server enabled
- Server works perfectly when tested independently
- Other MCP servers (projects) receive tool calls fine
9 Comments
Found 3 possible duplicate issues:
This issue will be automatically closed as a duplicate in 3 days.
🤖 Generated with Claude Code
It’s the same on Windows. On my home machine and a second remote machine running a different version of Claude Desktop that I haven’t touched since Thursday, so somehow it’s server-side.
Agree, this is a serious regression in Claude Desktop around MCPs. Here's a growing reddit thread about it.
https://www.reddit.com/r/ClaudeAI/comments/1qsdq58/claude_desktop_new_mcp_ui_bug_tools_freeze_until/
Image shows un-sent MCP tool call.
<img width="620" height="182" alt="Image" src="https://github.com/user-attachments/assets/c06318e1-a079-43ec-9ecf-e64a3f11ebbb" />
hope they will fix it soon
I've been experiencing the exact same issue and spent the whole day doing a thorough investigation. Sharing my findings here to help narrow down the root cause.
My Environment
line-desktop-mcp) + official@modelcontextprotocol/server-filesystemKey Finding: This is NOT a client-side bug
I downgraded Claude Desktop all the way back to 1.0.x — the exact same symptoms persist. This rules out a client-side regression and strongly points to a server-side (Anthropic backend) change made around Feb 1–2, 2026.
Log Evidence
Inspecting
%APPDATA%\Claude\logs\<mcp-server-name>.log:tools/callJSON-RPC request in the log at all. The client simply never dispatches it.tools/callrequest appears immediately, server processes it normally, result displays correctly.The MCP server itself is functioning perfectly — the issue is that the client never sends the request until the user interacts with the UI.
Came here to report similar findings. Tempted to vibecode an OCR/AHK app that clicks any unexpanded tool blocks. Feels like complete overkill for an issue that should have been addressed days ago.
You're right that it's not a desktop specific issue but it was affecting internal MCPs that are only used on desktop. We turned off a feature flag that was potentially causing the issue. Can you try again and see if it's working?
Really apologize for the disruption and appreciate you guys for taking the time to report the issue!
Awesome @alicelovescake , you rock, thanks! It's totally working now
This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.