cURL, a common tool for testing API endpoints, cannot be used to test and debug WebSocket connections because it's designed for unidirectional HTTP request-response connections, whereas WebSockets operate on bidirectional full-duplex connections. To debug WebSockets, developers can use alternative tools that support WebSocket connections, such as Hoppscotch.io, Online WebSocket Tester, Smart WebSocket Client, WebSocket King, and Postman's WebSocket Tool. These tools enable developers to establish the full-duplex connection required for WebSocket communication, allowing them to test and debug their real-time applications more effectively.