ConcertoNotes 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.