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

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.