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Params is an object used by the WebSocket constructor. The Params object contains request-specific options, such as headers that should be inserted into the connection initialization request.

Params.compressionstringCompression algorithm to be used by the WebSocket connection. The only supported algorithm currently is deflate.
Params.jarhttp.CookieJarThe cookie jar that will be used when making the initial HTTP request to establish the WebSocket connection. If empty, the default VU cookie jar will be used.
Params.headersobjectCustom HTTP headers in key-value pairs that will be added to the initial HTTP request to establish the WebSocket connection. Keys are header names and values are header values.
Params.tagsobjectCustom metric tags in key-value pairs where the keys are names of tags and the values are tag values. The WebSocket connection will generate metrics samples with these tags attached, allowing users to filter the results data or set thresholds on sub-metrics.

Example of custom metadata headers and tags

A k6 script that makes a WebSocket request with a custom header and tags results data with a specific tag

import { WebSocket } from 'k6/experimental/websockets';
export default function () {
const url = 'ws://localhost:10000';
const params = {
headers: { 'X-MyHeader': 'k6test' },
tags: { k6test: 'yes' },
const ws = new WebSocket(url, null, params);
ws.onopen = () => {
console.log('WebSocket connection established!');

The preceding example uses a WebSocket echo server, which you can run with the following command:

$ docker run --detach --rm --name ws-echo-server -p 10000:8080 jmalloc/echo-server