WebSocket is a communication protocol that provides full-duplex, persistent connections between a client and a server over a single TCP connection. Unlike HTTP, which follows a request-response pattern, WebSocket allows both parties to send data at any time. It starts with an HTTP upgrade handshake, then switches to the WebSocket protocol (ws:// or wss:// for encrypted). This makes it ideal for real-time applications like chat, live notifications, gaming, and financial tickers.

ws:// is the unencrypted WebSocket protocol (similar to HTTP), while wss:// is the encrypted version using TLS/SSL (similar to HTTPS). wss:// is strongly recommended for production environments, especially when transmitting sensitive data. Most modern browsers also require wss:// when the page is served over HTTPS due to mixed content policies. This tool supports both protocols.

Use this WebSocket Test Client to connect to your server. Enter your WebSocket URL (e.g., wss://your-domain.com/ws), click Connect, and send test messages. A successful connection will show a green indicator. You can send any text or JSON payload and observe the server's response in the message log. If the connection fails, check the error message in the log, verify your server is running, and ensure there are no firewall or CORS issues blocking the WebSocket handshake.

• Connection Refused: Server not running or wrong port.
• SSL/TLS Error: Certificate issues with wss:// — verify your SSL certificate.
• Mixed Content: Cannot use ws:// from an HTTPS page — upgrade to wss://.
• Timeout: Network latency or server not responding — check firewall rules.
• 1006 Abnormal Closure: Often a network issue or server crash — check server logs.
• Subprotocol Mismatch: Ensure client and server agree on the subprotocol.

WebSocket messages are transmitted as strings or binary data. To send JSON, use JSON.stringify() on your object before sending. When receiving, parse the string with JSON.parse(). This tool automatically detects JSON messages — if a received message is valid JSON, it will be displayed with syntax highlighting for easy reading. You can paste JSON directly into the input field and use the Format JSON button to prettify it before sending.

WebSocket: Full-duplex, low latency, ideal for bidirectional real-time communication (chat, gaming).
SSE (Server-Sent Events): Server-to-client only, simpler to implement, uses standard HTTP, good for live feeds and notifications.
HTTP Polling: Client repeatedly requests updates, higher latency and overhead, suitable for infrequent updates. WebSocket is the best choice when you need real-time, two-way communication with minimal overhead.

WebSocket subprotocols define a specific messaging format or convention on top of the raw WebSocket protocol. Common examples include MQTT (for IoT), STOMP (Simple Text Oriented Messaging Protocol), SOAP, and WAMP. The client specifies desired subprotocols during the handshake, and the server selects one from the list. You can specify a subprotocol in the optional field above when connecting.

Implement an exponential backoff reconnection strategy: on disconnect, wait for a short delay (e.g., 1 second), then attempt to reconnect. If that fails, double the delay (2s, 4s, 8s...) up to a maximum (e.g., 30 seconds). This prevents overwhelming the server while ensuring recovery. Also track the number of retry attempts and notify the user. For production apps, consider libraries like reconnecting-websocket or implement a custom reconnect manager with event listeners for online/offline browser events.