Claude AI desktop no longer connecting to Blender MCP server?

Claude AI Desktop Loses Connection to Blender MCP Server: A Deep Dive

Users of the Blender MCP (Model Context Protocol) addon have reported an issue where Claude AI Desktop unexpectedly loses its connection to the Blender MCP server. This manifests as Claude Desktop being unable to access the Blender scene data, rendering the integration unusable. The problem seems intermittent and can be difficult to diagnose, leading to significant frustration for users relying on this workflow.

Possible Root Causes

Several factors appear to contribute to this connectivity problem. The community discussion highlights a few key areas:

• Breaking Changes in python-sdk: A merged breaking change in the modelcontextprotocol/python-sdk repository (specifically, PR #1198) seems to be a major culprit. A patch release introduced an incompatibility, potentially affecting users who recently downloaded or installed Blender-MCP. This underscores the importance of version locking dependencies.
• Dependency Conflicts: The use of uvx (likely a tool for managing virtual environments and dependencies) might introduce conflicts if not configured correctly. The suggested temporary fix involving a requirements.txt file points to versioning issues with the mcp package itself.
• Claude Desktop Configuration: The configuration within Claude Desktop itself can be a source of problems. Claude may not correctly detect or maintain the connection to the Blender MCP server, requiring manual intervention to re-establish the link. This involves explicitly adding the Blender MCP server as a custom MCP tool within Claude's settings.
• Potential for Plagiarism: One user suggested that the newest updated CherryStudio application might be a plagiarism for Claude Desktop, potentially sharing the same kernel and thus the same issues.

Solutions and Workarounds

Based on the community's experiences, here are several steps to try and resolve the connection issue:

1. Reconfigure Blender MCP in Claude Desktop:

   Manually add the Blender MCP server as a custom tool:

   • Go to Claude's Settings → Features → MCP Tools.
   • Add a new connection with the following details:
     • Type: MCP Server
     • URL: http://localhost:9876
     • Name: Blender MCP

   After adding the server, reload the MCP configuration in Blender (File > Developer > Reload MCP Config) and restart both Blender and Claude Desktop.

2. Pin MCP Version with uvx:

   If you're using uvx, create a requirements.txt file containing:

   mcp==1.12.2

   Then, modify your mcpServers configuration to include the --with-requirements flag:

   {
       "mcpServers": {
           "blender": {
               "command": "uvx",
               "args": [
                   "--with-requirements=requirements.txt",
                   "blender-mcp"
               ],
               "env": {}
           }
       }
   }

   Alternatively, use the UV_CONSTRAINT environment variable to enforce the dependency:

   {
       "mcpServers": {
           "blender": {
               "command": "uvx",
               "args": [
                   "blender-mcp"
               ],
                "env": {
                       "UV_CONSTRAINT": "requirements.txt"
                     }
           }
       }
   }

3. Check Firewall and Port:

   Ensure that no firewall is blocking connections to port 9876 (the default port for the Blender MCP server).

4. Reinstall Blender-MCP:

   Uninstall and reinstall the Blender-MCP addon within Blender. Save preferences and restart Blender after reinstallation.

Practical Considerations and Best Practices

• Version Locking: This incident highlights the critical need for version locking dependencies in your development environment. Use tools like pip freeze > requirements.txt or similar mechanisms in your environment manager to ensure consistent behavior across installations.
• Logging and Error Reporting: Implement robust logging within the Blender MCP addon to capture detailed error messages. This will aid in diagnosing future connectivity issues.
• Stay Updated: Monitor the blender-mcp and python-sdk repositories for updates and bug fixes related to connectivity issues.
• Community Engagement: Actively participate in the Blender MCP community forums or issue trackers to share your experiences and contribute to finding solutions.