cron-and-intervals

name	cron-and-intervals
description	Use when building a val that runs on a schedule — periodic jobs, recurring tasks, polling, cron jobs, monitoring, alerting. Covers the interval handler signature, cron expressions, the UTC timezone constraint, and the `lastRunAt` pattern for detecting new items since the previous run.
triggers	["cron","interval","scheduled","schedule","recurring","periodic","timer","poll","polling","job","daily","hourly"]

Cron / Interval Vals

Interval vals (fileType: "interval") run on a recurring schedule defined by a cron expression. Use them for polling external APIs, sending reminders, running cleanups, generating reports, or any work that should happen on a clock rather than in response to a request.

Basic handler

// Learn more: https://docs.val.town/vals/cron/
export default async function (interval: Interval) {
  // interval.lastRunAt: Date | undefined
  console.log(interval);
}

The file must have an export — export default for the handler.

Timezone

Cron expressions run in UTC. Convert any human-readable schedule (e.g. "9am Eastern") to UTC before writing the cron expression. Daylight savings is not handled — pick a UTC time that's close enough year-round.

The lastRunAt pattern

interval.lastRunAt is the timestamp of the previous successful run (or undefined on the first run). Use it to fetch only items created since the last run, instead of re-scanning everything:

export default async function (interval: Interval) {
  const since = interval.lastRunAt ?? new Date(Date.now() - 24 * 60 * 60 * 1000);
  const newItems = await fetchItemsSince(since);
  for (const item of newItems) {
    await handle(item);
  }
}

This makes the val idempotent against missed runs and avoids reprocessing.

Reading and updating the schedule

• read_interval_settings — fetch the current cron expression and active state of an interval file.
• write_interval_settings — change the cron expression or pause/resume an interval.

When to skip a template

For simple scheduled jobs, create a new val with a single interval-type file directly — no template needed. Templates are for more complex shapes (dashboards, AI agents, webhook + UI combos).

Verifying changes

After editing an interval val, use run_file to invoke the handler manually instead of waiting for the next scheduled run.