tests.ws

WebSocket Testing Tools Compared

websocket testing tools load-testing debugging

There are dozens of WebSocket testing tools available. Some run in the browser, some in the terminal, some are full test frameworks. Choosing the right WebSocket test tool depends on what you need: quick manual testing, automated test suites, or load testing.

This guide breaks down the most widely used tools by category, explains what each one does well (and where it falls short), and helps you pick the right tool for your situation.

Quick Comparison Table

ToolTypeFreeKey Feature
tests.ws Online TesterBrowserYesInstant testing, no install
HoppscotchBrowserYesOpen source, full API suite
PieSocket TesterBrowserYesSimple, minimal interface
PostmanPlatformFreemiumCollections, environments
tests.ws WebSocket ProxyExtensionFreemiumIntercept and modify WS traffic
wscatCLIYesQuick terminal testing
websocatCLIYesUnix pipes, scripting
Jest/Vitest + wsFrameworkYesUnit testing WS servers
PlaywrightFrameworkYesE2E browser testing
k6Load testingYesScripted load tests with thresholds
ArtilleryLoad testingYesYAML config, scenarios

Browser-Based Tools

Browser-based testers are the fastest way to connect to a WebSocket server and send messages. You open a page, type in your URL, and start testing. No installation, no configuration.

tests.ws Online WebSocket Tester

The tests.ws WebSocket Tester gives you a clean interface for connecting to any WebSocket endpoint. You can send text and binary frames, view message history with timestamps, and inspect connection details. It supports custom headers and subprotocols, which matters when your server requires authentication tokens or specific protocol negotiation.

The tool runs entirely in your browser. Your WebSocket traffic goes directly from your machine to the target server, not through a proxy.

Hoppscotch

Hoppscotch is an open-source API development platform with a dedicated WebSocket tab. If you already test REST APIs with Hoppscotch, the WebSocket support fits naturally into your workflow. You can save WebSocket connections alongside your HTTP requests, organize them into collections, and share them with your team.

The downside: Hoppscotch treats WebSocket as a secondary feature. The interface works, but it lacks advanced options like frame-level inspection or binary message editing.

PieSocket WebSocket Tester

PieSocket offers a minimal online tester. Type a URL, connect, send messages. It does exactly what you expect and nothing more. This is useful when you need a quick connectivity check and do not want to think about which tool to open.

It lacks saved history, authentication support, and binary frame handling.

Postman

Postman added WebSocket support in 2021. The Postman WebSocket feature lets you create a new WebSocket request, specify your URL, and send messages from the familiar Postman interface. The advantage is integration with Postman’s existing features: environments, variables, and collections. If your team already standardizes on Postman, this keeps everything in one place.

The WebSocket implementation is still maturing. You cannot write automated tests for WebSocket connections the way you can for HTTP requests in Postman, and the message history can become hard to navigate during long sessions.

When to Use Browser Tools

Pick a browser-based tool when you need to manually test a WebSocket endpoint during development. They are ideal for verifying that your server accepts connections, responds to specific messages correctly, and handles edge cases like malformed frames. You do not need to install anything, and you can share a URL with a teammate who needs to reproduce an issue.

Browser Extensions

Extensions sit between browser tools and CLI tools. They run inside your browser but can do things that standalone web pages cannot, like intercepting WebSocket traffic from other tabs.

tests.ws WebSocket Proxy

The tests.ws WebSocket Proxy extension intercepts WebSocket connections in your browser and lets you inspect, modify, and replay messages in real time. This is different from a standalone tester. Instead of creating new connections, you monitor and manipulate the connections that your application already makes.

This is particularly valuable for debugging. You can watch the exact messages your frontend sends to your backend, modify a message to test error handling, or replay a sequence of messages to reproduce a bug. The extension works with any website or web application without requiring code changes.

Other Extensions

Several Chrome extensions offer basic WebSocket inspection. The Chrome DevTools Network tab itself shows WebSocket frames, though the interface is limited. Extensions like “WebSocket King Client” provide a testing interface similar to browser-based tools but accessible from the browser toolbar.

When Extensions Beat Browser Tools

Extensions are better than standalone browser tools when you need to debug an existing application. A browser tester creates new connections from scratch. An extension watches the connections your app already makes. If you are trying to figure out why your chat application drops messages or why your real-time dashboard shows stale data, an extension that can intercept live WebSocket traffic will save you significant time compared to recreating the scenario in a separate tester.

Command-Line Tools

CLI tools give you speed and scriptability. You can pipe output, chain commands, and integrate WebSocket testing into shell scripts and CI pipelines.

wscat

wscat is the most popular WebSocket CLI tool. It is maintained by the team behind the ws library for Node.js.

Install it with npm:

npm install -g wscat

Connect to a server:

wscat -c ws://localhost:8080

Send a message:

> {"action": "subscribe", "channel": "prices"}

wscat keeps the connection open and prints every message the server sends. You type messages and press Enter to send them. It supports custom headers via the -H flag:

wscat -c ws://localhost:8080 -H "Authorization: Bearer your-token"

wscat covers 80% of terminal WebSocket needs. Where it falls short is scripting. You cannot easily pipe a sequence of messages into wscat and capture responses programmatically.

websocat

websocat fills the gaps that wscat leaves. Written in Rust, it treats WebSocket connections as bidirectional streams that play nicely with Unix pipes.

Install via Cargo:

cargo install websocat

Or download a prebuilt binary from the GitHub releases page.

Connect and send messages:

echo '{"action": "ping"}' | websocat ws://localhost:8080

Pipe a file of messages:

cat messages.txt | websocat ws://localhost:8080

Forward a local TCP port to a WebSocket:

websocat -b ws-l:127.0.0.1:1234 tcp:127.0.0.1:5678

websocat supports TLS, binary frames, autoreconnect, and dozens of other options. The learning curve is steeper than wscat, but the flexibility makes it the better choice for automation and scripting.

wsta

wsta is a lightweight alternative written in Rust. It focuses on simplicity: connect, send, receive. If websocat feels too complex for your needs and wscat is not available (or you prefer not to install Node.js), wsta is a solid middle ground.

wsta ws://localhost:8080

Development on wsta has slowed in recent years. For new projects, websocat is generally the better choice.

When to Use CLI Tools

Use CLI tools when you work primarily in the terminal, need to script WebSocket interactions, or want to integrate quick tests into shell-based workflows. They are also useful in environments where you cannot run a browser, like SSH sessions into remote servers. For quick checks during development, wscat is hard to beat. For anything involving pipes, files, or automation, reach for websocat.

API Testing Platforms

Platforms combine WebSocket testing with broader API testing capabilities. They make sense when WebSocket is one part of a larger API surface.

Postman

Postman’s WebSocket support lets you create WebSocket requests alongside REST, GraphQL, and gRPC requests in the same collection. You define environments with variables (like {{ws_url}}), and those variables work in WebSocket requests just as they do in HTTP requests.

To test a WebSocket endpoint in Postman:

  1. Click “New” and select “WebSocket Request”
  2. Enter your WebSocket URL
  3. Add any headers or query parameters
  4. Click “Connect”
  5. Type messages in the composer and click “Send”

The message log shows sent and received frames with timestamps. You can save specific messages as examples for documentation.

Postman’s limitation: no scripted assertions for WebSocket responses. You can send messages and view responses, but you cannot write test scripts that verify the content of incoming frames the way you can with HTTP response tests.

Insomnia

Insomnia added WebSocket support as well. The experience is similar to Postman: create a WebSocket request, connect, send messages, view responses. Insomnia’s interface is slightly cleaner for WebSocket work, though it has fewer collaboration features than Postman.

If your team already uses Insomnia for API development, the WebSocket tab keeps your tooling consolidated.

When to Use Platforms

Use an API testing platform when your application exposes both HTTP and WebSocket endpoints and you want to manage all your API tests in one tool. The shared environment variables and collection organization justify the overhead of a heavier application.

Test Frameworks

When manual testing is not enough, you need automated tests. These frameworks let you write code that connects to WebSocket servers, sends messages, asserts on responses, and runs as part of your CI/CD pipeline.

Jest or Vitest with the ws Library

For Node.js WebSocket servers, the most straightforward approach is testing with Jest or Vitest and the ws library.

import { WebSocketServer } from 'ws';
import WebSocket from 'ws';
import { describe, it, expect, beforeAll, afterAll } from 'vitest';

let server;
let port;

beforeAll(() => {
  return new Promise((resolve) => {
    server = new WebSocketServer({ port: 0 });
    server.on('listening', () => {
      port = server.address().port;
      resolve();
    });
    server.on('connection', (ws) => {
      ws.on('message', (data) => {
        ws.send(`echo: ${data}`);
      });
    });
  });
});

afterAll(() => {
  server.close();
});

describe('WebSocket server', () => {
  it('echoes messages back', () => {
    return new Promise((resolve) => {
      const client = new WebSocket(`ws://localhost:${port}`);
      client.on('open', () => {
        client.send('hello');
      });
      client.on('message', (data) => {
        expect(data.toString()).toBe('echo: hello');
        client.close();
        resolve();
      });
    });
  });
});

This approach gives you full control. You start the server, create clients, send messages, and assert on responses. The tests run fast because everything is in-process.

The downside: you test the WebSocket protocol layer but not the full browser experience. If your frontend uses a library like Socket.IO that adds its own protocol on top of WebSocket, you need to account for that in your test setup.

Playwright and Puppeteer

For end-to-end testing that includes WebSocket connections, Playwright and Puppeteer run a real browser. Your tests navigate to your application, and the browser establishes WebSocket connections just as a real user’s browser would.

Playwright example:

import { test, expect } from '@playwright/test';

test('receives real-time updates', async ({ page }) => {
  await page.goto('http://localhost:3000/dashboard');

  // Wait for WebSocket data to appear in the UI
  await expect(page.locator('.live-price')).not.toBeEmpty();

  // Verify the price updates
  const firstPrice = await page.locator('.live-price').textContent();
  await page.waitForTimeout(2000);
  const secondPrice = await page.locator('.live-price').textContent();

  // Price should have changed
  expect(firstPrice).not.toBe(secondPrice);
});

Playwright also lets you intercept WebSocket connections at the protocol level using page.on('websocket'), which is useful for verifying that specific messages are sent or received. If your testing needs go beyond what browser DevTools offer, you can also use the tests.ws WebSocket Proxy extension alongside your test runner.

When to Use Frameworks

Use test frameworks when you need repeatable, automated verification of WebSocket behavior. Unit tests with Jest or Vitest catch regressions in your server logic. E2E tests with Playwright catch integration issues between your frontend and backend. Both should run in CI on every pull request.

Load Testing Tools

Production WebSocket servers need to handle thousands of concurrent connections. Load testing tools simulate this traffic and measure how your server performs under pressure.

k6

k6 has a built-in WebSocket module that lets you script realistic WebSocket load tests in JavaScript.

import ws from 'k6/ws';
import { check } from 'k6';

export const options = {
  stages: [
    { duration: '30s', target: 100 },
    { duration: '1m', target: 500 },
    { duration: '30s', target: 0 },
  ],
};

export default function () {
  const url = 'ws://localhost:8080/ws';
  const res = ws.connect(url, {}, function (socket) {
    socket.on('open', () => {
      socket.send(JSON.stringify({ action: 'subscribe', channel: 'updates' }));
    });

    socket.on('message', (data) => {
      const msg = JSON.parse(data);
      check(msg, {
        'has type field': (m) => m.type !== undefined,
        'is valid update': (m) => m.type === 'update',
      });
    });

    socket.setTimeout(function () {
      socket.close();
    }, 60000);
  });

  check(res, { 'status is 101': (r) => r && r.status === 101 });
}

k6 excels at scripted scenarios with built-in thresholds. You define pass/fail criteria directly in your test configuration. The output integrates with Grafana, Datadog, and other monitoring platforms.

k6’s limitation: the JavaScript runtime is not full Node.js. You cannot import arbitrary npm packages. If your WebSocket protocol requires a specific client library, you may need to work around this constraint.

Artillery

Artillery uses YAML configuration files to define load test scenarios.

config:
  target: "ws://localhost:8080"
  phases:
    - duration: 60
      arrivalRate: 10
  engines:
    ws: {}

scenarios:
  - engine: ws
    flow:
      - send: '{"action": "subscribe", "channel": "updates"}'
      - think: 1
      - send: '{"action": "ping"}'
      - think: 5

Run the test:

npx artillery run websocket-load-test.yml

Artillery is easier to get started with than k6 for simple scenarios. The YAML format is readable and does not require programming knowledge. For more advanced logic, Artillery supports JavaScript functions within scenarios.

Artillery is less flexible than k6 for complex test logic and has fewer built-in assertion options.

Gatling

Gatling is a JVM-based load testing tool with WebSocket protocol support. If your team already uses Gatling for HTTP load testing, adding WebSocket scenarios keeps your load testing stack unified. Gatling’s DSL is written in Scala, which can be a barrier if your team is not familiar with JVM languages.

Gatling produces detailed HTML reports out of the box, including percentile response times and request-per-second charts.

Locust with websocket-client

Python developers often prefer Locust for load testing. Locust does not have native WebSocket support, but you can add it with the websocket-client package.

from locust import User, task, between
import websocket

class WebSocketUser(User):
    wait_time = between(1, 3)

    def on_start(self):
        self.ws = websocket.create_connection("ws://localhost:8080/ws")

    def on_stop(self):
        self.ws.close()

    @task
    def send_message(self):
        self.ws.send('{"action": "ping"}')
        result = self.ws.recv()

This approach works but requires more manual setup than k6 or Artillery. You handle connection management, error handling, and metrics collection yourself. Locust’s strength is its Python flexibility. If your test logic requires complex data generation or external service calls, Python gives you access to the full ecosystem.

Load Testing Comparison

For most teams, k6 is the best starting point for WebSocket load testing. It offers the right balance of scripting power and ease of use, with good CI/CD integration.

Choose Artillery if you prefer YAML configuration and your scenarios are straightforward. Choose Gatling if your team already uses it for HTTP tests. Choose Locust if your team writes Python and needs maximum flexibility. For a deeper look at setting up these tools, see the load testing WebSocket guide.

Choosing the Right Tool

Your choice depends on your primary use case.

Manual testing during development: Start with the tests.ws WebSocket Tester for quick checks. If you need to debug traffic in an existing application, install the WebSocket Proxy extension. For terminal work, install wscat.

Automated testing in CI/CD: Write unit tests with Jest or Vitest and the ws library. Add Playwright E2E tests for critical user flows that depend on WebSocket connections. Both run reliably in CI environments.

Load testing before launch: Use k6 for scripted load tests with thresholds and assertions. Start with a small number of connections and ramp up. Monitor your server’s CPU, memory, and connection count as you increase load.

Debugging production issues: The browser extension approach wins here. You can inspect live traffic without modifying your application code. Combine it with your server-side logs to trace messages end to end.

Team collaboration: If your team needs to share test configurations, Postman collections or Artillery YAML files check into version control and work across operating systems.

Most teams end up using two or three tools from different categories. A browser-based tester for quick manual checks, a test framework for CI, and a load testing tool for performance validation. That combination covers the full testing lifecycle without unnecessary complexity.