The @postman/mcp-server package uses [email protected] which prints log messages to stdout instead of stderr. This contaminates the JSON-RPC communication channel when using Claude Desktop, generating repeated “Invalid JSON-RPC message” errors on every startup.
The fix is simple: change console.log to console.error for the dotenv initialization output, or configure dotenv with { quiet: true }.
Environment: Windows 11, Claude Desktop, npx -y @postman/mcp-server