Hi Luca,
The Web API has no HTTP server primitive (that's only in the C# API, via WebServerExtension + IWebServer.AddRoute()).
Express won't help either — Web extensions run inside Studio Pro's webview, which can't bind listening ports.
I would highly recommend you to use the MCP server that is given by mendix itself. Check out this video for configuration : https://www.linkedin.com/posts/vishnuprasath011_mendix-claudecode-mcp-activity-7458417875352170496-m_C2?utm_source=share&utm_medium=member_desktop&rcm=ACoAADmzNMYBeN4cjtlEUpYl8Gt2q0FppuFduaY