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Get an email alert when your website goes down

The usual answer is to sign up for an uptime monitoring service. On Val Town it's one cron-triggered val: fetch your URL on a schedule, remember the last known status in blob storage, and send yourself an email with std/email only when the status changes — one email when the site goes down, one when it recovers.

The monitor

Section titled “The monitor”

View and run this example on Val Town

import { blob } from "https://esm.town/v/std/blob/main.ts";
import { email } from "https://esm.town/v/std/email";


// The URL to monitor. Change this to your website.
const URL_TO_MONITOR = "https://example.com";


export default async function () {
  let up = false;
  let detail = "";
  try {
    const res = await fetch(URL_TO_MONITOR);
    up = res.ok;
    detail = `HTTP ${res.status}`;
  } catch (e) {
    detail = String(e);
  }


  const last = await blob.getJSON("last-status") as { up: boolean } | undefined;
  if (last?.up === up) return; // no change, stay quiet


  await blob.setJSON("last-status", { up });
  if (last === undefined) return; // first run: just record the baseline


  await email({
    subject: up
      ? `Recovered: ${URL_TO_MONITOR} is back up (${detail})`
      : `Down: ${URL_TO_MONITOR} (${detail})`,
    text: `${URL_TO_MONITOR} is ${up ? "back up" : "down"}. ${detail}`,
  });
}

Because the last status is stored in blob storage, you never get repeat alerts while the site stays down. The first run only records a baseline, so remixing it never sends a surprise email.

Set it up

Section titled “Set it up”
  1. Remix this template — click the Remix button in the top right corner.
  2. In monitor.ts, change URL_TO_MONITOR to your website's URL.

That's it: no API keys, no environment variables, no signup for a monitoring service. To test it, point URL_TO_MONITOR at a URL that 404s and click Run on monitor.ts twice — the first run records the baseline, the second one emails you.

Notes

Section titled “Notes”
  • Alerts go to your Val Town account email — that's where std/email delivers by default.
  • The template checks every five minutes (*/5 * * * *). On the free plan crons run at most once every 15 minutes, so change the schedule to */15 * * * * (or upgrade to Pro for up to once a minute).
  • A response is counted as up when res.ok is true (status 200–299), and as down on any other status or a network error.

Next steps

Section titled “Next steps”