[Bug] MCP tool works and responds, but Claude Desktop pop-up shows "Could not attach to MCP server"

[jigarvyasidea]

Description

Everything is working properly:

• MCP server is running
• Configuration is valid
• The tool works and gives correct responses when tested directly

The MCP tool itself is functioning fine.
But in Claude Desktop pop-up, it still shows:

So the tool is usable, but the Desktop client UI wrongly shows this error.

---

Steps to Reproduce

1. Start MCP server (works fine independently).
2. Add configuration in claude_desktop_config.json.
3. Restart Claude Desktop.
4. Test the tool → it responds correctly.
5. Open Desktop pop-up → error message appears:

---

Expected Behavior

Claude Desktop should:

• Attach to the MCP server without error

---

Actual Behavior

• MCP tool works and returns responses
• But the Claude Desktop pop-up shows only an error message:

---

Additional Notes

• Everything else works perfectly, only the pop-up shows a misleading error
• Tool calls and responses are successful despite the error
• Tried restart, absolute paths, different transports → still same result

[LuluBeatson]

Hi @jigarvyasidea, please could you provide your server config and the error message or screenshot

[sharukphoenix]

hey there! I'm facing the same issue(not really an one though but that pop up is a lil annoying). I connected to the mcp server via Docker's MCP Toolkit and I didn't mess with the MCP server config as Docker does it all by default.

The pop-up :

This is the claude mcp config file :

I hope someone fixes it.
Thanks :)