Fixing 500 Error in MCP Server | Generated by AI

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The error you’re encountering is a 500 internal server error from a local API endpoint at http://127.0.0.1:3456, which appears to be a Model Context Protocol (MCP) server. This is commonly used to bridge local large language models (LLMs) like those managed by Ollama to applications such as Claude Desktop, VS Code extensions (e.g., Copilot), or IDEs like Cursor for AI-assisted coding tasks. The underlying JavaScript/TypeScript error—”Cannot read properties of undefined (reading ‘includes’)”—suggests the server code is attempting to access the .includes() method on a variable that’s undefined or null, likely during request processing, response handling, or interaction with Ollama.

This issue often arises when the API is called to analyze or fix code (in this case, your recommend_posts.py script), but the server fails due to a configuration problem, missing dependencies, or an unexpected response from the backend LLM.

Steps to Troubleshoot and Fix

  1. Verify Ollama is Running and Configured:
    • Ollama (the local LLM engine) is typically the backend for MCP servers. Ensure it’s installed and running on its default port (11434).
    • Test it by running curl http://localhost:11434/api/tags in your terminal. This should list installed models. If it fails or returns an empty list, install a model with ollama pull <model-name> (e.g., ollama pull llama3).
    • If Ollama isn’t responding, start it with ollama serve and confirm no port conflicts.
  2. Restart the MCP Server:
    • The MCP server on port 3456 might be in a bad state. Kill the process: kill -9 $(lsof -t -i:3456).
    • Restart it according to your setup (e.g., if using a tool like ollama-mcp, run the start command from its documentation). Check for startup logs indicating successful connection to Ollama.
  3. Check for Port Conflicts or Claude Desktop Interference:
    • Claude Desktop (if installed) often uses port 3456 for authentication or MCP. If it’s running, close the app or kill its process as above.
    • If you’re using Cursor or VS Code, confirm your settings.json has the correct API base URL and no typos. Temporarily switch to a different port by setting an environment variable like PORT=4567 when starting the MCP server, then update your API base to match.
  4. Update Software and Check Logs:
    • Update Ollama: ollama update.
    • If using a specific MCP bridge (e.g., from GitHub repos like emgeee/mcp-ollama or patruff/ollama-mcp-bridge), pull the latest version and rebuild/reinstall.
    • Run the MCP server with verbose logging (add flags like --debug if supported) and inspect the output for clues about what’s undefined (e.g., a missing response from Ollama or invalid request payload).
    • In Cursor or your IDE, check the developer console (Ctrl+Shift+I in Cursor) for additional error details.
  5. Test the API Directly:
    • Simulate a simple request to the API using curl: curl -X POST http://127.0.0.1:3456/v1/chat/completions -H "Content-Type: application/json" -d '{"model": "your-model-name", "messages": [{"role": "user", "content": "Hello"}]}'.
    • If it returns the same 500 error, the issue is server-side. If it works, the problem might be specific to how your IDE formats requests (e.g., malformed payload when including file contents).
  6. Workarounds:
    • Switch to a direct Ollama OpenAI-compatible endpoint: Set your API base to http://127.0.0.1:11434/v1 (Ollama supports this) and bypass MCP if not needed for advanced context features.
    • Use a different MCP implementation or tool. For example, try a minimal Ollama setup without MCP for code fixing.
    • If this is in Cursor, fall back to cloud-based models (e.g., Claude via official API) temporarily by removing the custom base URL.
    • Reinstall dependencies: If your MCP server uses Node.js, run npm install in its directory to fix any missing modules.

If these don’t resolve it, the error might stem from a bug in your specific MCP bridge version, especially if handling file contents or post recommendations triggers it. Search GitHub issues for your exact MCP repo with the error message, or open a new issue with your setup details.

Failed to register Ollama model: TypeError: Cannot read properties of undefined (reading ‘includes’)
Ollama MCP Server on GitHub
Model Context Protocol Documentation
Ollama Documentation

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