I've successfully used Fiddler Classic as alternative to Charles to look at live websocket traffic when debugging things before. Websocket support in general is a bit of a hidden feature though since you need to go to the request that established the connection and double-click the websocket logo to the left on it, which opens a new panel showing its traffic.

The newer "Fiddler Everywhere" might also be able to do it, possibly even better, but I dislike the UI and I'm used to Classic so I've stuck to that.