Comparison
WebSocket debugging tools, sorted by the problem they solve
Most “best WebSocket tool” lists mix three different categories of software that don't compete with each other at all. Before comparing features, answer one question — it eliminates two thirds of the list immediately.
Whose traffic are you looking at? Traffic you generate yourself needs a client. Traffic your application already exchanges needs an inspector. Traffic below the browser needs a proxy.
The three categories
You open the connection and send frames
Postman, Firecamp, Hoppscotch Realtime, Insomnia, wscat, websocat.
The right tool when you're building or testing a server: you control the payload, replay it, save it in a collection, share it with the team. Useless when the bug is in how your front-end reacts to what the server sent, because you're not the front-end — you're a second client with a different session.
You watch the connection your page already has
Chrome DevTools' Network → WS panel, and browser extensions that add a DevTools panel: Wirepeek, WebSocket Visualizer.
The right tool when the bug is in your application's own session — real auth, real state, real timing. You can't reproduce it from a fresh client connection because the interesting part is what the app did before things went wrong.
You capture below the browser
Wireshark, mitmproxy, Charles.
The right tool when the problem is under the WebSocket layer: the HTTP upgrade being stripped by a proxy, a TLS handshake failing, TCP window issues — or when the client isn't a browser at all (a mobile app, an IoT device, a server-to-server connection). Costs setup: for wss:// you need to export TLS session keys via SSLKEYLOGFILE, or install a root certificate.
Side by side
| Capability | Client | DevTools | Inspector extension | Proxy |
|---|---|---|---|---|
| See your app's real session | no | yes | yes | yes |
| Send your own frames | yes | no | no | with scripting |
| Capture before you opened it | n/a | no | yes | yes |
| Decode socket.io framing | Postman, partly | no | yes | no |
| Decode binary payloads | no | hex only | yes | with dissectors |
| Traffic from non-browser clients | n/a | no | no | yes |
| Below-WebSocket problems (TLS, TCP) | no | no | no | yes |
| Setup cost | none | none | install | certs, keylog |
When each one is the wrong choice
Don't use a client when…
…the question is “why did my page get this”. A client gives you a clean second connection with its own session and its own timing. If the bug depends on the sequence your app went through — a reconnect, an expired token, a race between two events — you will not reproduce it there.
Don't use a proxy when…
…the traffic is ordinary browser wss:// and the question is about payload content. You'll spend the afternoon on certificates and keylog files to end up looking at the same bytes DevTools already had, minus the protocol decoding.
Don't use an inspector extension when…
…you need to send anything. Wirepeek is read-only by design: it observes, it doesn't replay or modify. If your job today is “hit the server with this payload and see what comes back”, install Postman and be done in two minutes. The same applies if the client isn't a browser — an extension can't see traffic from a mobile app or a background service.
Don't use plain DevTools when…
…the connection opened before you pressed F12, or the payloads are encoded. The Network tab records from the moment it opens and shows frames as the wire carries them — protocol framing included. It's the fastest answer for a quick look at plain-JSON traffic, and the wrong answer for a handshake bug.
Two inspector extensions
If you land in the inspector category, there are two maintained Chrome options, and they're built around different priorities.
WebSocket Visualizer formats JSON messages, keeps a bounded history per connection and includes a hex viewer for binary frames. Straightforward, and if your traffic is plain JSON it's all you need.
Wirepeek puts the effort into decoding: socket.io/engine.io framing into event names, JSON nested inside string fields, JWT, base64, gzip, deflate, LZ4, MessagePack, CBOR, Thrift Compact, and JSON embedded in binary frames. It hooks WebSocket.prototype in the page's main world at document_start, so it captures from the handshake and survives reloads. Every decoder is strict — it either consumes the whole payload or hands the frame back raw — and payloads that look encrypted are flagged rather than guessed at.
Both are free and read-only. Neither will send a frame for you.
If the inspector column is the one you need
Wirepeek is a free Chrome DevTools panel: capture from document_start, decode, filter, search inside decoded content, export the session. No account, no backend, capture is opt-in per tab and nothing leaves your machine.