Add MCP Server to Retell AI agent throws 500 server error

Support Help
1

Hello Retell CS team,

I want to add my MCP server to Retell AI agent. My MCP server URL is https://elwmwne53c.execute-api.us-west-2.amazonaws.com/dev/mcp The MCP server is up and running.

You can also verify by running the curl command: curl``https://elwmwne53c.execute-api.us-west-2.amazonaws.com/dev/mcp

I tested it Claude Desktop, it works perfectly. When I try to add the MCP server to Retell AI, I get a 500 Internal Server Error. This MCP server is very important for the voice agent, we are developing.

2

I understand you’re encountering a 500 Internal Server Error when trying to add your MCP server to Retell AI. This appears to be a backend issue on Retell’s side.(1)

To add your MCP server to Retell AI, you should:(2)(3)

  1. Click on + Add MCP in your agent configuration(2)
  2. Enter your MCP server URL in the MCP Server Endpoint field(2)(3)
  3. Optionally set custom request headers and query parameters(2)
  4. Select the MCP tool from the list of available tools(2)
  5. Save the MCP Tool(2)

When you add your MCP server and no tools appear, it usually means the server isn’t exposing the MCP spec correctly.(1) Retell won’t show anything unless your MCP returns a valid capabilities + tools structure.(1)

A valid MCP endpoint should return a JSON response that includes both capabilities and tools.(4) Here’s the expected format:(4)

{
  "capabilities": {
    "tools": true
  },
  "tools": [
    {
      "name": "getUser",
      "description": "Fetches a user by ID",
      "input_schema": {
        "type": "object",
        "properties": {
          "id": { "type": "string" }
        },
        "required": ["id"]
      }
    }
  ]
}

(4)

Since you’re experiencing a 500 error and your MCP server works with Claude Desktop, I recommend:

  1. Verify your MCP server returns the proper JSON structure shown above
  2. Check that your server exposes the proper endpoints that Retell AI can call(2)(3)
  3. If the issue persists, contact Retell support directly

For support, you can: