WebSocket exchange rate API

// Node.js 22+ · run on your server · set EXCHANGERATE_API_KEY in the environment
const key = process.env.EXCHANGERATE_API_KEY;
if (!key) throw new Error("EXCHANGERATE_API_KEY is required");

let retries = 0;
let stopped = false;
function connect() {
  const ws = new WebSocket("wss://api.exchangerate.dev/v1/stream");
  ws.addEventListener("open", () => {
    ws.send(JSON.stringify({ action: "auth", api_key: key }));
  });
  ws.addEventListener("message", ({ data }) => {
    const frame = JSON.parse(String(data));
    if (frame.type === "authenticated") {
      retries = 0;
      ws.send(JSON.stringify({ action: "subscribe", base: "USD", symbols: ["EUR", "JPY"] }));
    } else if (frame.type === "snapshot" || frame.type === "update") {
      if (frame.stale) return; // Keep the observation time; don't treat it as a fresh tick.
      console.log(frame.base, frame.symbol, frame.rate, frame.effective_at);
    } else if (frame.type === "state") {
      console.log(frame.base, frame.symbol, frame.state); // stale or unavailable
    } else if (frame.type === "error") {
      console.error(frame.code, frame.message);
      if (["invalid_api_key", "quota_exceeded", "connection_limit_exceeded", "subscription_limit_exceeded"].includes(frame.code)) {
        stopped = true;
        ws.close();
      }
    }
  });
  ws.addEventListener("close", () => {
    if (stopped) return;
    const delay = Math.min(30_000, 1_000 * 2 ** Math.min(retries++, 5));
    setTimeout(connect, delay + Math.random() * 250);
  });
}
connect();

{
  "type": "update",
  "base": "USD",
  "symbol": "JPY",
  "rate": "154.792",
  "effective_at": "2026-09-15T02:59:44Z",
  "source": "live",
  "source_type": "market",
  "market_session": "open",
  "derived": false,
  "stale": false
}