Summary
Experimental MCP server (ModelContextProtocol.StartServer) starts successfully on port 8000 but instantly drops connections with external tools (Claude, Cursor, Roo Code, VS code )
What Type of Bug are you experiencing?
Editor
Steps to Reproduce
Go to the plugins section in UE 5.8 and turn on Unreal MCP and MCP Client Toolset. Restart the engine.
Open the output log console and type ModelContextProtocol.StartServer. It says all listeners started on port 8000 and generates a config file.
Try to connect any standard MCP tool to it. I tried Claude Desktop with the generated config, Cursor settings via HTTP, and VS Code with Roo Code using an HTTP-to-SSE proxy command.
Watch the connection drop instantly
Expected Result
Expected Result
The server should actually hold the connection so external LLMs or IDE extensions can read the UE data
Observed Result
As a result, the connection either fails or is immediately lost
Roo Code and VS Code display the error “Connection closed Error -32000”
Affects Versions
5.8
Platform(s)
Windows
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For crash reports, include your callstack
No crash
Additional Notes
This feature looks like it’s going to be really cool. To be honest, I’m not sure if it’s a bug, since I haven’t found a single guide for these plugins, and all I’ve heard about this feature is what was mentioned in the presentation. I’m not sure if it’s even supposed to work right now, but I wanted to give it a try anyway.