WebSocket Tester & Debugger
Connect to WebSocket servers, send and receive messages, inspect JSON payloads, and monitor connection statistics. Free, private, browser-based WebSocket client.
How to Use
The WebSocket Tester is a browser-based debugging client for testing WebSocket connections in real time. It lets you connect to any WebSocket server, send and receive messages, inspect JSON payloads with syntax highlighting, and monitor connection statistics -- all without installing desktop software or browser extensions.
How to use this tool
- Enter a WebSocket URL: Type or paste a WebSocket server address (wss:// for encrypted connections). The tool includes quick-access buttons for popular echo servers to test with immediately.
- Add subprotocols (optional): If your server requires specific subprotocols, enter them comma-separated in the protocols field. These are sent during the WebSocket handshake.
- Click Connect: The status indicator shows connection state in real time -- gray for disconnected, yellow pulsing for connecting, green for connected, and red for errors.
- Send messages: Type your message in the composer area and click Send or press Enter. Switch between Text and JSON format modes. JSON mode enables auto-formatting and the Prettify button.
- Inspect the message log: All sent, received, and system messages appear in the scrollable log with timestamps, direction indicators, and byte sizes. JSON messages are automatically detected and syntax-highlighted.
- Monitor statistics: The stats bar shows messages sent and received, total bytes transferred, connection duration, and round-trip latency when using echo servers.
About This Tool
What Is the WebSocket Protocol?
WebSocket is a communication protocol defined in RFC 6455 that provides full-duplex, bidirectional channels over a single TCP connection. Unlike HTTP, where the client must initiate every request, WebSocket allows both client and server to push data independently at any time. The connection begins as an HTTP/1.1 request with an Upgrade header. If the server supports WebSocket, it responds with HTTP 101 (Switching Protocols), and both sides switch from HTTP framing to WebSocket framing on the same TCP socket. From that point, either side can send text or binary frames with minimal overhead -- just 2 to 14 bytes of framing per message compared to hundreds of bytes of HTTP headers.
WebSocket vs HTTP: When to Use Each
HTTP is request-response: the client sends a request, the server returns a response, and the connection is done. This model works well for fetching web pages, REST APIs, and file downloads. WebSocket excels when you need real-time data flow in both directions: live chat applications, multiplayer games, financial ticker feeds, collaborative editing, IoT sensor dashboards, and live notifications. Server-Sent Events (SSE) occupy a middle ground -- they provide server-to-client streaming over HTTP but lack bidirectional communication. Choose WebSocket when you need sub-100ms message delivery with minimal overhead, your application requires server-initiated messages, or you need to send data in both directions simultaneously.
The WebSocket Handshake
Every WebSocket connection starts with an HTTP upgrade handshake. The client sends Connection: Upgrade and Upgrade: websocket headers along with a random Sec-WebSocket-Key. The server concatenates this key with a fixed GUID, computes a SHA-1 hash, and returns it as Sec-WebSocket-Accept. This exchange proves both sides understand the WebSocket protocol and prevents accidental upgrades from non-WebSocket clients. Subprotocols like graphql-ws or mqtt can be negotiated during this handshake using the Sec-WebSocket-Protocol header. Use the cURL to Code converter to inspect raw HTTP upgrade requests.
Common Use Cases
WebSocket powers some of the most interactive applications on the web. Chat platforms like Slack and Discord use WebSocket for instant message delivery. Financial platforms stream real-time stock quotes and cryptocurrency prices. Multiplayer games rely on WebSocket for low-latency game state synchronization. Collaborative tools like Google Docs use WebSocket for operational transformation, allowing multiple users to edit simultaneously. DevOps dashboards use WebSocket to stream log output and metrics. IoT platforms connect thousands of sensors through WebSocket gateways. Use the JSON Formatter to inspect structured WebSocket payloads, or the Base64 decoder to decode encoded message content.
Why Use This Tool
Zero Installation Required
Traditional WebSocket testing requires installing desktop clients like Postman, Insomnia, or wscat. This tool runs entirely in your browser -- open the page, paste a URL, and connect. There is nothing to install, no accounts to create, and no CLI dependencies to manage. It works on any device with a modern browser, including tablets and Chromebooks where installing native applications may not be an option.
Direct Browser Connection
This tool connects directly from your browser to the WebSocket server you specify. There is no proxy server, no relay, and no middleman intercepting your messages. This means your data travels directly between your browser and your server, making it safe for testing with authentication tokens, API keys, and sensitive payloads. The browser's native WebSocket API handles all connection management, TLS encryption, and frame encoding. Parse your connection URLs with the URL Parser, or validate server endpoints with the URL Validator.
Built-In JSON Intelligence
Most WebSocket APIs exchange JSON-encoded messages. This tester automatically detects JSON in both sent and received messages, applies syntax coloring with distinct colors for keys, strings, numbers, booleans, and null values, and formats them with proper indentation. The JSON format mode in the message composer lets you write JSON with auto-prettification before sending. Combined with the JSON Formatter for deeper analysis and the JSON Validator for syntax checking, DevToolkit provides a complete JSON debugging workflow.