Claude AI desktop no longer connecting to Blender MCP server?

Claude AI Desktop Loses Connection to Blender MCP Server

Users of the Blender MCP (Model Context Protocol) addon are reporting an issue where Claude AI Desktop unexpectedly loses its connection to the Blender MCP server. This prevents Claude from accessing and analyzing the Blender scene context, disrupting workflows that rely on this integration. The issue seems to appear suddenly, without any apparent changes to the Blender MCP setup.

Possible Root Causes

Several factors appear to contribute to this connectivity problem:

Breaking Changes in python-sdk: A merged breaking change in the modelcontextprotocol/python-sdk repository (specifically, PR #1198) may be causing compatibility issues. This change was introduced in a patch release, potentially affecting users who recently installed or updated Blender-MCP.
Dependency Versioning: The Blender MCP addon might not be locked to a specific version of the mcp dependency. This can lead to unpredictable behavior when the underlying mcp library is updated with breaking changes.
Claude Desktop Configuration: Claude Desktop might not be correctly configured to recognize and connect to the Blender MCP server. This could involve incorrect URL settings, firewall issues, or problems with the MCP service within Claude Desktop.
Potential Conflicts with Other Applications: Some users suspect that applications similar to Claude Desktop might interfere with the Blender MCP connection.

Solutions and Workarounds

Here are several approaches to resolve the Blender MCP connection issue in Claude AI Desktop:

Reconfigure Claude Desktop Connection:
Ensure that Claude Desktop is explicitly configured to connect to the Blender MCP server. This involves adding a new connection with the following parameters:
- Type: MCP Server
- URL: http://localhost:9876
- Name: Blender MCP
After adding the connection, test it within Claude's settings to verify connectivity.
Reload MCP Configuration in Blender:
Within Blender, navigate to File > Developer > Reload MCP Config. This forces Blender to refresh its MCP configuration, which may resolve connection issues.
Reinstall Blender MCP Addon:
Uninstall and reinstall the Blender MCP addon within Blender's preferences. Save preferences and restart Blender after reinstalling. This ensures that the addon is properly installed and configured.

Pin mcp Dependency Version (Temporary Fix for uvx users):

Create a requirements.txt file containing the following:

mcp==1.12.2

Then, modify the uvx command in your configuration to include --with-requirements=requirements.txt as the first argument. For example:

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

Manual Configuration Update:
Some users have reported success by manually updating the configuration file, ensuring the correct path to the blender-mcp executable is specified:
```
"blender": {
  "command": "/Users/USERNAME/.local/bin/blender-mcp",
  "args": [],
  "env": {
  }
}
```
Remember to replace /Users/USERNAME/.local/bin/blender-mcp with the actual path to your blender-mcp executable.

Practical Tips and Considerations

Firewall: Ensure that your firewall is not blocking connections to port 9876, the default port for the Blender MCP server.
Blender MCP Server Status: Verify that the Blender MCP server is running within Blender and is listening on the correct port.
Dependency Management: Consider using a virtual environment to manage the dependencies of the Blender MCP addon, which can help prevent conflicts and ensure consistent behavior.
Report the Issue: If none of these solutions work, report the issue to the Blender MCP developers with detailed information about your setup, including Blender version, MCP addon version, and any error messages.