WebSocket Tester – Online WebSocket Client, Latency & Frame Inspector
WebSocket Tester
Connect to WebSocket endpoints (ws:// or wss://) in real time to inspect frames, measure latency, test heartbeats, and debug payloads.
A developer-first WebSocket testing tool and client running directly in your browser. Connect to any ws:// or wss:// endpoint with sub-protocol support, custom JSON/text payloads, auto-reconnect, automated heartbeat keep-alive pings, frame logging, JSON inspection, and latency benchmarking. No signup required.
Keywords: websocket tester, websocket client online, test websocket connection, ws client, wss tester, websocket debugger, websocket echo, websocket frame inspector
Tags: websocket, network, api, realtime, streaming, debugging, json-rpc, graphql-ws
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WebSocket Tester is also known as: WebSocket Client, WebSocket Debugger, WS / WSS Inspector, WebSocket Echo Tester.
How to WebSocket Tester Online
Enter your WebSocket target URL in the endpoint bar at the top (e.g., wss://echo.websocket.org, wss://ws.postman-echo.com/raw, or ws://localhost:8080).
Optionally configure WebSocket sub-protocols (such as graphql-ws or soap) and auto-reconnect settings via the Settings popover.
Click Connect or press Cmd+Enter to initiate the live WebSocket handshake directly from your browser.
Compose JSON, text, or binary frames in the Message Composer, or choose a ready-to-use template from the Templates library (Echo, JSON-RPC 2.0, GraphQL Subscriptions, Chat events, or Market Ticker).
Click Send or press Cmd+Shift+Enter to transmit frames in real time and inspect live incoming messages and system events in the Frame Log.
Monitor real-time connection metrics including round-trip message latency (RTT), session uptime, sent/received byte totals, and export complete session transcripts as JSON or plain text.
WebSocket Tester Features
Direct browser-native WebSocket client supporting unencrypted ws:// and secure TLS/SSL wss:// endpoints with zero backend proxy lag.
Full WebSocket subprotocols negotiation support via Sec-WebSocket-Protocol (e.g., graphql-ws, graphql-transport-ws, soap, chat).
Automated heartbeat keep-alive ping runner with configurable interval and custom payload to prevent idle TCP connection timeouts.
Intelligent auto-reconnection with configurable retry intervals, attempt caps, and active reconnection status badges.
Live frame stream logging with color-coded direction badges (↑ Sent, ↓ Received, ℹ System Events, ⚠ Errors).
High-resolution round-trip message latency (RTT) calculation and benchmarking (min, max, average, and latest latency).
Interactive message inspector modal featuring syntax-highlighted JSON tree formatting, raw text view, and one-click replay.
One-click JSON formatting, syntax validation, and character counting in the payload editor.
Extensive Payload Template library for JSON-RPC 2.0 requests, GraphQL WS subscriptions, chat room broadcasts, and crypto tickers.
Real-time frame search and multi-criteria filtering (filter by text query, direction, frame type, or error status).
Multi-language code generator providing copy-paste client connection snippets for Browser JS, Node.js (ws), Python (websockets), Go (gorilla/websocket), Rust (tokio-tungstenite), and CLI (websocat).
Export session transcripts as structured JSON reports (.json) or timestamped plain text log files (.log) for CI/CD or post-mortem debugging.
Quick-select preset public echo endpoints (Postman Echo, Echo.websocket.org, SocketsBay) and common localhost configurations.
Full keyboard workflow: Cmd+Enter to connect/disconnect, Cmd+Shift+Enter to send payload, Cmd+Shift+K to clear log, and Cmd+Shift+H to toggle heartbeat.
100% client-side execution — connection packets and authentication tokens never touch external servers or third-party storage.
Persistent user preferences and draft payloads saved locally in your browser via localStorage.
Supported SQL Dialects
The WebSocket Tester supports 6 SQL dialects. Select the right dialect for accurate formatting and keyword recognition.
- Plain WebSocket (ws:// - RFC 6455)
- Standard unencrypted bi-directional WebSocket connection over TCP port 80. Ideal for local development servers and internal microservices.
- Secure WebSocket (wss:// - RFC 6455 & TLS)
- Encrypted WebSocket connection running over TLS/SSL on TCP port 443. Required for production web applications and public real-time streaming endpoints.
- GraphQL over WebSocket (graphql-ws)
- Modern official subprotocol for executing GraphQL subscriptions and live queries with connection_init and subscribe frame lifecycles.
- Legacy Apollo Subscriptions (subscriptions-transport-ws)
- Legacy protocol for Apollo Server and client GraphQL real-time event streaming.
- JSON-RPC 2.0 over WebSocket
- Standard stateless remote procedure call specification for Ethereum/Web3 RPC nodes, Language Server Protocol (LSP), and distributed backends.
- STOMP / Event Stream over WebSocket
- Simple Text Oriented Messaging Protocol commonly used with Spring Boot WebSockets, RabbitMQ, and ActiveMQ brokers.
Frequently Asked Questions
- What is WebSocket and how does the HTTP Upgrade handshake work?
- WebSocket is a full-duplex, persistent communication protocol standardized under RFC 6455. Unlike HTTP request-response cycles where each interaction requires a new TCP handshake and header overhead, a WebSocket connection begins with a standard HTTP GET request containing "Upgrade: websocket" and "Connection: Upgrade" headers. Once the server responds with HTTP status 101 Switching Protocols, the TCP connection remains open for instantaneous, low-latency, bidirectional message exchange.
- What is the difference between ws:// and wss://?
- ws:// represents an unencrypted WebSocket connection transmitted over plain TCP (default port 80), similar to HTTP. wss:// represents a secure WebSocket connection encrypted via Transport Layer Security (TLS/SSL, default port 443), similar to HTTPS. In modern web browsers, connecting to remote ws:// endpoints from a page served over HTTPS is blocked by browser mixed-content security rules. However, local development endpoints (such as ws://localhost:8080 or ws://127.0.0.1:3000) are treated as secure contexts by modern browsers and remain accessible.
- Can I test local WebSocket servers running on localhost?
- Yes! Because the WebSocket client runs directly in your browser without passing through a cloud proxy, you can connect to local servers such as ws://localhost:8080, ws://localhost:3000/ws, or any local network IP address (e.g. ws://192.168.1.50:8000). Ensure your local backend server is running and configured to accept connections.
- How do WebSocket subprotocols work?
- During the initial WebSocket handshake, the client can advertise one or more subprotocols via the Sec-WebSocket-Protocol header (such as graphql-ws, soap, or custom application protocols). The server inspects the requested protocols and selects one to use for the session. In DevFlow WebSocket Tester, you can add custom subprotocols in the settings popover and verify the negotiated protocol reported in the connection event log.
- What do standard WebSocket close codes mean?
- Close codes are 16-bit integers defined by RFC 6455 indicating why a connection closed. Common codes include: 1000 (Normal Closure — purposeful termination), 1001 (Going Away — server restart or client navigation), 1002 (Protocol Error), 1003 (Unsupported Data), 1006 (Abnormal Closure — dropped connection without close frame, TLS failure, or network disruption), 1008 (Policy Violation), and 1011 (Internal Server Error). Our frame inspector displays the exact close code, reason text, and clean-close status.
- Why do WebSocket connections drop after 30 to 60 seconds?
- Intermediate network infrastructure such as cloud load balancers (AWS ALB, Google Cloud LB), reverse proxies (Nginx, Envoy, Cloudflare), and mobile cellular gateways automatically terminate idle TCP connections that have no traffic for 30–60 seconds. Enabling the automated Heartbeat in this tool periodically sends a lightweight ping frame (e.g., {"type": "ping"}) to keep the connection active and prevent timeout terminations.
- How does latency (RTT) measurement work in this tool?
- When you transmit a message or heartbeat ping, the tester captures a high-resolution timestamp. When the server transmits an echo or response frame, the client calculates the elapsed round-trip time (RTT) in milliseconds. The metrics bar tracks your latest RTT alongside running minimum, maximum, and average latency benchmarks across the entire session.
- How does CORS apply to WebSockets compared to HTTP REST APIs?
- The browser Same-Origin Policy (SOP) and Cross-Origin Resource Sharing (CORS) headers apply strictly to HTTP requests, not WebSocket connections. The browser always includes the "Origin" header during the WebSocket upgrade handshake. It is the responsibility of the WebSocket server to validate the Origin header and reject unauthorized origins. Unlike REST API testing in browsers, WebSockets can connect to cross-origin endpoints directly without requiring a server-side proxy.
- Can I send authentication tokens with WebSocket connections?
- Browsers do not allow custom HTTP request headers (such as "Authorization: Bearer <token>") to be set directly via the native JavaScript WebSocket API. Instead, WebSocket authentication is typically handled through: 1) Query parameters in the URL (e.g., wss://api.example.com/ws?token=xyz), 2) Subprotocols (e.g., ["bearer", "my-token"]), or 3) An initial authentication message frame sent immediately after the onopen event (such as connection_init in GraphQL WS).
- Are my WebSocket messages and credentials private?
- Yes, completely. All WebSocket connections are established directly between your browser and the target WebSocket server. No message payloads, URLs, headers, or authentication tokens are routed through, stored on, or logged by DevFlow servers.
- Can I export the session message log for documentation or debugging?
- Yes. Click the Export button at the top right of the Frame Log to download your complete session history. You can export as a structured JSON file (.json) containing all metadata, timing, and frame contents, or as a timestamped plain-text log file (.log).
- How can I generate client connection code for my backend or CLI?
- Click the "Client Code" button in the connection bar to open the Code Snippets modal. You can copy ready-to-run WebSocket client code for Browser JavaScript, Node.js (ws), Python (websockets), Go (gorilla/websocket), Rust (tokio-tungstenite), and the websocat command-line utility.
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