Windows: ERR_UNSUPPORTED_ESM_URL_SCHEME when running in Claude Desktop #26
Description
When trying to use reddit-mcp-buddy in Claude Desktop on Windows, the MCP server fails to start with the following
error:
Error [ERR_UNSUPPORTED_ESM_URL_SCHEME]: Only URLs with a scheme in: file, data, and node are supported by the
default ESM loader. On Windows, absolute paths must be valid file:// URLs. Received protocol 'c:'
at throwIfUnsupportedURLScheme (node:internal/modules/esm/load:184:11)
at defaultLoad (node:internal/modules/esm/load:82:3)
at ModuleLoader.load (node:internal/modules/esm/loader:803:12)
at ModuleLoader.loadAndTranslate (node:internal/modules/esm/loader:582:43)
Environment:
- OS: Windows
- Node.js version: v22.18.0
- npm version: 11.5.2
- reddit-mcp-buddy version: v1.1.6
- Installation method: npm install -g reddit-mcp-buddy
Claude Desktop Configuration (claude_desktop_config.json):
Tried both configurations:
"reddit-mcp-buddy": {
"command": "reddit-mcp-buddy"
}
and
"reddit-mcp-buddy": {
"command": "npx",
"args": ["-y", "reddit-mcp-buddy"]
}
Both result in the same error.
Full error log:
2025-10-04T07:52:09.435Z [reddit-mcp-buddy] [info] Message from client:
{"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"claude-ai"
,"version":"0.1.0"}},"jsonrpc":"2.0","id":0}
Failed to start server: Error [ERR_UNSUPPORTED_ESM_URL_SCHEME]: Only URLs with a scheme in: file, data, and node
are supported by the default ESM loader. On Windows, absolute paths must be valid file:// URLs. Received protocol
'c:'
Expected behavior: MCP server starts successfully and connects to Claude Desktop
Actual behavior: Server crashes immediately with ESM URL scheme error related to Windows path handling (C: drive
paths not being recognized as valid file:// URLs)
Additional context: This appears to be a Windows-specific path handling issue with ESM modules. Windows absolute
paths (e.g., C:\path\to\file) need to be converted to file:///C:/path/to/file format for the ESM loader.