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mcp-websocket-invalid-url ​

MCP WebSocket transport URL must be valid

Error

Rule Details ​

This rule checks that the url field of MCP servers with type "websocket" is a valid URL by attempting to parse it with the URL constructor. URLs containing variable expansions (${ or $) are skipped since they are resolved at runtime. An invalid URL will prevent Claude Code from establishing a WebSocket connection to the MCP server.

Incorrect ​

WebSocket server with a malformed URL

json
{
  "mcpServers": {
    "realtime": {
      "type": "websocket",
      "url": "not-a-valid-url"
    }
  }
}

Correct ​

WebSocket server with a valid URL

json
{
  "mcpServers": {
    "realtime": {
      "type": "websocket",
      "url": "wss://mcp.example.com/ws"
    }
  }
}

WebSocket server with a variable-expanded URL (skipped)

json
{
  "mcpServers": {
    "realtime": {
      "type": "websocket",
      "url": "${MCP_WS_URL}"
    }
  }
}

How To Fix ​

Provide a fully qualified URL with a ws:// or wss:// scheme. Ensure the URL is well-formed and reachable from the environment where Claude Code runs.

Options ​

This rule does not have any configuration options.

Resources ​

Version ​

Available since: v0.2.0