WebSocket mock server

Updated October 18, 2026Free mock REST & WebSocket APIs

Need a realtime backend for a chat, ticker or notification UI? Use the public echo server, or publish a scripted WebSocket mock that greets clients, pushes events on a timer and answers messages by pattern.

Echo server

const ws = new WebSocket("wss://mockfox.dev/api/ws/echo");
ws.onmessage = (e) => console.log("echo:", e.data);
ws.onopen = () => ws.send("hello");

Open the echo server in the WebSocket tester →

Scripted WebSocket mock

Add a ws block to any mock. After publishing, connect to wss://mockfox.dev/api/ws/m/<id>.

Template

Mock definition (JSON)

{
  "name": "Price ticker",
  "resources": [
    {
      "name": "symbols",
      "items": [
        {
          "id": 1,
          "symbol": "ACME",
          "name": "Acme Corp"
        },
        {
          "id": 2,
          "symbol": "GLBX",
          "name": "Globex"
        }
      ]
    }
  ],
  "routes": [],
  "ws": {
    "echo": false,
    "onConnect": [
      {
        "type": "hello",
        "message": "Send {\"type\":\"subscribe\",\"symbol\":\"ACME\"}"
      }
    ],
    "replies": [
      {
        "match": "subscribe",
        "reply": {
          "type": "subscribed",
          "ok": true
        }
      },
      {
        "match": "ping",
        "reply": "pong"
      }
    ],
    "interval": {
      "everyMs": 2000,
      "messages": [
        {
          "type": "tick",
          "symbol": "ACME",
          "price": 101.25
        },
        {
          "type": "tick",
          "symbol": "ACME",
          "price": 101.4
        },
        {
          "type": "tick",
          "symbol": "ACME",
          "price": 100.95
        }
      ]
    }
  }
}

✓ Valid — 1 resources, 0 custom routes, WebSocket script

Script reference

Field	What it does
`onConnect`	Messages sent as soon as a client connects
`interval`	`{ everyMs, messages }` — pushes the messages in a loop (min 1 s)
`replies`	`{ match, reply }` rules; `match` is a substring or `/regex/flags`
`echo`	Echo messages that match no rule

Related tools

Frequently asked questions

Is MockFox free?

Yes. No sign-up, no API key. Fair-use rate limits keep it fast for everyone, and clearly labeled sponsors pay for the servers.

What is the echo server URL?

wss://mockfox.dev/api/ws/echo — every text or binary message you send is sent straight back.

How long can a connection stay open?

Sessions close after 10 minutes; reconnect to continue. Messages are limited to 64 KB.

Can replies depend on the message?

Yes. Each reply rule matches a substring or a /regex/ and sends any JSON or text back.

Your business here? Sponsor this tool from $16/week. See placements