When I try to connect to localhost, I get this error, but when I use 127.0.0.1 instead, everything is fine. I guess websocat can't resolve names or something? curl can talk to the server running on localhost just fine.
Would be cool to have this fixed for ease of use. And thank you for the tool, it does seem to work quite well otherwise 👍

E.g.:

user@hostname $ websocat ws://localhost:8080/ws
websocat: WebSocketError: I/O failure
websocat: error running

user@hostname $ websocat ws://127.0.0.1:8080/ws
# no error

user@hostname $ curl localhost:8080/ws
# no error