IconVault's WebSocket Frames inspector lets you build raw WebSocket frames byte by byte according to RFC 6455 and decode hex dumps back into their fields. Choose the opcode (text, binary, close, ping, pong, continuation), set FIN and mask flags, supply a payload, and get the exact bytes a client would put on the wire, or paste hex and see it broken down into header fields and decoded payload.

It is built for developers debugging custom WebSocket implementations, proxies and protocol stacks, where seeing the actual framing matters more than a high-level client. Everything is computed in your browser with nothing uploaded, and it is free with no signup. Honest note: this inspects protocol framing only; it does not open real connections, for that use a WebSocket client or sandbox tool.