Why can’t I set an Authorization header? How do I pass a token?

The browser WebSocket API does not allow custom handshake headers — a browser restriction no web tool can bypass. Common workarounds are a token in the URL query (wss://example.com/ws?token=…), passing it through a subprotocol (Sec-WebSocket-Protocol), or relying on a same-site cookie. Sending an authentication message right after connecting is also a common pattern.

The connection fails but shows no reason. What should I check?

For security, browsers do not reveal why a WebSocket connection failed; the page only gets error and close events (often code 1006). Check the URL and port, that the server is running, that the wss certificate is valid, whether the server validates the Origin header, and remember that an https page cannot connect to plain ws:// (it is blocked as mixed content). The browser DevTools console and network panel usually show more detail.

Can I test a local WebSocket server?

Yes for wss://. For ws://localhost, some browsers such as Chrome relax the mixed-content rule for localhost, so it often connects directly. If it is blocked, give your local server a self-signed certificate and use wss://, or run a similar tool from a local http page.

What is the difference between SSE and WebSocket?

WebSocket is full-duplex: client and server can send messages at any time, which suits chat, games and collaborative editing. SSE (Server-Sent Events) runs over plain HTTP and only lets the server push text events, but it is simpler and has built-in reconnection and event IDs, which suits notifications, log streams and streaming AI output. To test SSE the server must respond with text/event-stream and allow CORS.

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🔌WebSocket Tester Online - Connect to ws/wss, Send Messages, Heartbeat and SSE Testing

When you build chat, live prices, collaborative editing or other real-time features, you need a handy WebSocket client to connect to your server and send messages by hand. Enter a ws:// or wss:// URL (with optional subprotocols) and connect; the status and the negotiated subprotocol and extensions are shown live. Send text, JSON (validated as you type, with one-click formatting and optional minifying) or binary messages entered as hex and sent as an ArrayBuffer, with Ctrl / ⌘ + Enter to send. The message log shows direction, millisecond timestamps and byte size, displays binary messages as a hex + ASCII dump and can pretty-print JSON; filter it by content or direction and export it as JSON or TXT. You can also auto-reconnect with exponential backoff, send a heartbeat message on an interval and save frequent messages as templates stored in your browser. The SSE tab tests Server-Sent Events: open an EventSource, listen for custom event names and see lastEventId. Connections go straight from your browser and never pass through this site. Note that the browser WebSocket API cannot set custom headers such as Authorization.

Free · No sign-up · Runs in your browserLast updated: 2026-10-26

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How to use WebSocket Tester

1Enter a ws:// or wss:// URL, add subprotocols if needed and click Connect
2Choose text, JSON or binary (hex), type a message and send it
3Watch the message log, filter or export it, and enable auto-reconnect or heartbeat as needed

FAQ

Why can’t I set an Authorization header? How do I pass a token?: The browser WebSocket API does not allow custom handshake headers — a browser restriction no web tool can bypass. Common workarounds are a token in the URL query (wss://example.com/ws?token=…), passing it through a subprotocol (Sec-WebSocket-Protocol), or relying on a same-site cookie. Sending an authentication message right after connecting is also a common pattern.
The connection fails but shows no reason. What should I check?: For security, browsers do not reveal why a WebSocket connection failed; the page only gets error and close events (often code 1006). Check the URL and port, that the server is running, that the wss certificate is valid, whether the server validates the Origin header, and remember that an https page cannot connect to plain ws:// (it is blocked as mixed content). The browser DevTools console and network panel usually show more detail.
Can I test a local WebSocket server?: Yes for wss://. For ws://localhost, some browsers such as Chrome relax the mixed-content rule for localhost, so it often connects directly. If it is blocked, give your local server a self-signed certificate and use wss://, or run a similar tool from a local http page.
What is the difference between SSE and WebSocket?: WebSocket is full-duplex: client and server can send messages at any time, which suits chat, games and collaborative editing. SSE (Server-Sent Events) runs over plain HTTP and only lets the server push text events, but it is simpler and has built-in reconnection and event IDs, which suits notifications, log streams and streaming AI output. To test SSE the server must respond with text/event-stream and allow CORS.