WebSocket Tester

WebSocket Tester - Test Real-Time WebSocket Connections

WebSocket is the protocol that finally gave browsers two-way real-time communication, standardised in 2011 as RFC 6455 and now ubiquitous: every modern chat app, live-sports widget, collaborative document editor (Figma, Google Docs), trading platform tick feed, GraphQL subscription, multiplayer game lobby, and most real-time notification systems run on top of it. Unlike the HTTP request-response cycle, a WebSocket connection stays open after the initial handshake, lets either party send a frame at any moment, and survives proxies and corporate firewalls because it starts as a regular HTTP Upgrade request before switching protocols. Debugging WebSocket apps is harder than debugging HTTP, though — browsers' DevTools network tab shows you the handshake but is poor at visualising the message stream over time. This tester fills that gap. Type any ws:// or wss:// URL, click Connect, and you have a persistent live channel: send arbitrary text or JSON messages with the Send button, watch every server-sent frame appear in real time with a precise timestamp, and identify message direction (sent / received / system events like open/close/error) by color in the log. Useful for poking at echo.websocket.org during a tutorial, validating that your backend's broadcast loop actually reaches connected clients, reproducing race conditions, or watching the heartbeat traffic of a service you're integrating with. For performance work it goes beyond a toy echo client: a built-in round-trip time (RTT) panel times the milliseconds between each sent JSON frame and the next received reply using performance.now(), then tracks latest, min, average and max latency alongside sent/received counters — so you can spot jitter, a slow broker, or a backend that stopped echoing at a glance.

What is a WebSocket?

WebSocket is a protocol that provides full-duplex communication channels over a single TCP connection. Unlike HTTP, which is request-response based, WebSocket allows:

- Real-time bidirectional communication
- Persistent connection between client and server
- Lower latency than polling
- Efficient for real-time applications

Common uses:
- Chat applications
- Live feeds and notifications
- Real-time gaming
- Collaborative editing
- Live sports scores
- Stock tickers

WebSocket URLs use ws:// (insecure) or wss:// (secure with TLS) protocols.

How do I test a WebSocket?

Testing a WebSocket is simple:

1. Enter the WebSocket URL (ws:// or wss://)
2. Click 'Connect' to establish connection
3. Wait for 'Connected' status
4. Type a message in the message field
5. Click 'Send' to send the message
6. View responses in the message history
7. Click 'Disconnect' when done

Example WebSocket servers for testing:
- ws://echo.websocket.org (echoes back messages)
- wss://echo.websocket.org (secure echo)

The message history shows all sent and received messages with timestamps.

How do I measure WebSocket latency (round-trip time)?

Connect to an echo or heartbeat endpoint and send a frame: the tool times the milliseconds between your sent message and the next received reply using the browser's high-resolution performance.now() clock, then displays the result in the Round-Trip Latency (RTT) panel.

The panel shows four live metrics:
- Latest: the most recent round-trip time in ms
- Avg: the running mean across every measured reply
- Min/Max: the fastest and slowest replies so far — the spread reveals jitter
- Sent/Received: total frame counters, so you can tell if the backend stopped echoing

Send several frames to build a sample. A steady low avg with a tight min/max means a healthy real-time feed; a climbing max or a received count that lags the sent count points to a slow broker, network jitter, or a backend that dropped the connection. This works best against echo/heartbeat endpoints where each sent frame produces one reply (e.g. wss://echo.websocket.org).

How do I test Socket.IO, SignalR, or STOMP endpoints?

Those are higher-level protocols layered on top of raw WebSocket, so a plain WebSocket client connects only if you speak their handshake.

Socket.IO: it is NOT a raw WebSocket. The transport URL looks like wss://host/socket.io/?EIO=4&transport=websocket, and frames are prefixed with Engine.IO/Socket.IO packet codes (e.g. 40 to open the default namespace, 42["event",payload] to emit). You can connect to that URL and manually type the packet-coded frames, but a dedicated Socket.IO client is easier for full sessions.

SignalR: connect to the negotiated URL with the connection token as a query param (…/hub?id=TOKEN). After connecting, send the JSON handshake {"protocol":"json","version":1} terminated by the ASCII record-separator character (\u001e) before any invocations.

STOMP: STOMP is a text frame protocol over WebSocket. After connecting, send a CONNECT frame (CONNECT\naccept-version:1.2\nhost:yourhost\n\n then a null byte), then SUBSCRIBE / SEND frames. Each frame ends with a null (\u0000) byte.

For all three, append any required auth or version query parameters directly to the URL, since browsers cannot set custom WebSocket headers.

How do I send and inspect JSON frames?

Most production WebSocket APIs exchange JSON, and this tester treats every frame as text, so you can paste a JSON payload straight into the message box and click Send.

Sending JSON:
- Type or paste a valid JSON object, e.g. {"type":"subscribe","channel":"prices"}
- The multi-line input lets you format payloads across several lines before sending
- Press Send (or Enter; Shift+Enter for a newline)

Inspecting replies:
- Received frames appear in the color-coded log with a precise timestamp
- Content is shown in a monospace font with preserved whitespace, so pretty-printed JSON stays readable
- To pretty-print a minified reply, copy it from the log into a dedicated JSON formatter

Tip: keep payloads well under 1 MB for snappy round-trips, and watch the RTT panel to confirm the server answered each JSON frame you sent.

What's the difference between ws:// and wss://?

ws:// and wss:// are similar to http:// and https://:

ws:// (WebSocket):
- Unencrypted connection
- Uses port 80 by default
- Data is transmitted in plain text
- Less secure
- Good for local development

wss:// (WebSocket Secure):
- Encrypted connection using TLS/SSL
- Uses port 443 by default
- Data is encrypted
- More secure
- Required for HTTPS websites
- Recommended for production

Modern browsers require wss:// when the webpage is served over HTTPS.

Why can't I connect to some WebSocket servers?

Connection failures can occur for several reasons:

1. CORS/Security: Server doesn't allow connections from browsers
2. Authentication: Server requires authentication headers
3. SSL/TLS: Mixed content (ws:// on HTTPS page)
4. Server Down: WebSocket server is offline
5. Firewall: Network firewall blocks WebSocket
6. Invalid URL: Wrong URL format or port

Troubleshooting:
- Check URL format (ws:// or wss://)
- Use wss:// on HTTPS pages
- Verify server is running
- Check server CORS settings
- Try echo.websocket.org for testing
- Check browser console for errors

What types of data can I send?

This WebSocket tester sends text messages. WebSocket supports:

Text Messages:
- Plain text
- JSON strings
- XML strings
- Any string format

Binary Messages:
- ArrayBuffer
- Blob
- File data
(Not supported in this simple tester)

Common formats:
- JSON: {"type": "message", "text": "Hello"}
- Plain text: "Hello, World!"
- Commands: "/join room123"

Most WebSocket APIs expect JSON format for structured data communication.

How is WebSocket different from Server-Sent Events (SSE) and long-polling?

All three deliver server pushes to a browser without polling, but with different tradeoffs. (1) WebSocket: full duplex (both sides talk anytime), low overhead per message (2-14 byte frame header), arbitrary text or binary payloads, custom application protocol. Best for chat, multiplayer games, collaborative editing — anything truly interactive. (2) Server-Sent Events: one-way only (server → client), simpler API (EventSource in browsers), automatic reconnection, plain UTF-8 text only. Best for live feeds where the client never talks back: stock prices, news tickers, server logs streaming. SSE goes over plain HTTP/2 so it's friendlier with intermediate proxies. (3) Long-polling: the client makes an HTTP request that the server holds open until data arrives, then immediately reopens. Highest latency and overhead but works everywhere because it's plain HTTP. Modern apps default to WebSocket; fall back to SSE for unidirectional feeds; long-polling only matters for legacy environments without proper proxy support.

What's the maximum message size and rate I can push through a WebSocket?

The protocol itself permits frames up to 2^63 bytes — effectively unlimited. The real limits come from your runtime stack. Browsers cap individual messages at around 64 MB before warning or disconnecting; the practical sweet spot for application-layer messages is under 1 MB to avoid choking single-threaded JavaScript event loops. Node.js 'ws' library defaults to a 100 MB maximum but is configurable. For rate, modern hardware sustains 100,000+ small messages per second per WebSocket connection on localhost, dropping to thousands/sec across the public internet depending on RTT. If you need higher throughput, batch small updates into larger periodic messages (e.g. 16ms cadence for 60fps clients), use binary framing (ArrayBuffer) instead of JSON to skip string parsing, and consider WebTransport (the HTTP/3-based successor designed for low-latency unreliable streams) for game-style traffic. Avoid sending massive base64-encoded blobs over WebSocket; use a separate HTTP upload and signal completion over the socket.

Is my data safe?

Privacy and security considerations:

- All connections go directly from your browser to the WebSocket server
- No data passes through our servers
- We don't log or store any messages
- Use wss:// for encrypted connections
- Avoid sending sensitive data to untrusted servers
- Test servers may log your messages

Best practices:
- Use wss:// in production
- Don't send passwords or sensitive data to public test servers
- Verify server authenticity
- Use authentication when required
- Test with dummy data when possible

Key Features

• Connect to any WebSocket server (ws:// or wss://)
• Send text messages in real-time
• Receive messages instantly
• View complete message history
• Timestamp for each message
• Color-coded message types (sent/received/system)
• Round-trip latency (RTT) panel: latest, min, avg, max in ms
• Sent/received frame counters to spot dropped echoes
• Connection status indicator
• Disconnect and reconnect easily
• Clear message history
• Copy messages to clipboard
• Dark mode support
• 100% client-side - direct browser-to-server connection
• No data logging or storage
• Mobile-friendly responsive design