WebSocket: run code from the browser

For real-time results without polling, connect via Socket.IO. The WebSocket server authenticates your API key, forwards code to the execution engine, and pushes results back instantly.

import { io } from "socket.io-client";

const socket = io("wss://api.onlinecompiler.io", {
  auth: { token: "YOUR_WIDGET_KEY" }
});

socket.on("connect", () => {
  socket.emit("runcode", {
    compiler: "python-3.14",
    code: 'print("Hello via WebSocket!")',
    input: ""
  });
});

socket.on("codeoutput", (result) => {
  console.log(result.output);    // "Hello via WebSocket!"
  console.log(result.error);     // ""
  console.log(result.status);    // "success"
  console.log(result.exit_code); // 0
  console.log(result.signal);    // null
  console.log(result.truncated); // false
  console.log(result.time);      // "0.0248"
  console.log(result.total);     // "0.0330"
  console.log(result.memory);    // "8192"
});

Connecting

Pass the widget key as auth.token when you connect. The connection is refused when the key is missing or inactive, when it is a REST API key, or when the key has an allowed domain and the page's origin isn't on it. Every run on the connection uses that key.

The runcode event

The codeoutput event

When the program has run, codeoutput carries the same fields as the sync endpoint's response: output, error, status, exit code, signal, truncated, run time, total time and memory. When the run couldn't start, it carries only error, with the reason: more than one run a second on the connection, an account limit, a request that isn't valid, or a queue that's unavailable.