By Flavio Copes

How to run a Cloudflare Worker on a schedule with Cron Triggers. Nightly jobs, periodic checks, and cleanups, with no server to keep running.

~~~

Not everything happens because someone visits a URL. Some things should just run on their own: a nightly report, a cleanup every hour, a check every five minutes.

For that, Cloudflare has Cron Triggers. You give a Worker a schedule, and Cloudflare runs it for you. No server sitting idle, no cron daemon to babysit.

Add a schedule

Schedules go in wrangler.jsonc, under triggers:

{
  "triggers": {
    "crons": ["0 2 * * *"]
  }
}

That string is a cron expression. 0 2 * * * means “every day at 2:00.” You can have more than one schedule in the array.

A few common ones:

• */5 * * * * — every 5 minutes
• 0 * * * * — every hour, on the hour
• 0 2 * * * — every day at 2:00
• 0 0 * * 1 — every Monday at midnight

If cron syntax makes your eyes glaze over, a tool like crontab.guru spells it out in plain English. I also built a free cron builder that does the same and previews the next run times.

Handle the schedule

A normal Worker has a fetch handler. A scheduled Worker has a scheduled handler instead (or as well):

export default {
  async scheduled(event, env, ctx) {
    console.log('Running the nightly job')
    // do the work here
  },
}

Cloudflare calls scheduled on your schedule. You get env with all your bindings, so you can read your database, write to storage, send email, whatever the job needs.

A real example

Here’s a nightly cleanup that deletes old rows from a D1 database:

export default {
  async scheduled(event, env, ctx) {
    const thirtyDaysAgo = Date.now() - 30 * 24 * 60 * 60 * 1000

    await env.DB.prepare(
      'delete from logs where created_at < ?'
    ).bind(thirtyDaysAgo).run()
  },
}

Set it to 0 2 * * * and your logs table cleans itself up every night while you sleep.

Be careful with time zones

Here’s the one thing that trips people up. Cron schedules run in UTC, not your local time.

So 0 9 * * * is 9:00 UTC, which might be the middle of the night where you are. If you want a job at 9:00 your time, convert to UTC first.

Long jobs and waitUntil

If your job kicks off work that shouldn’t block, wrap it in ctx.waitUntil so Cloudflare keeps the Worker alive until it finishes:

async scheduled(event, env, ctx) {
  ctx.waitUntil(generateDailyReport(env))
}

Testing it locally

You don’t want to wait until 2 AM to know if your job works. In dev, you can trigger it manually:

npx wrangler dev

Then in another terminal, hit the test endpoint Wrangler exposes:

curl "http://localhost:8787/cdn-cgi/handler/scheduled"

That runs your scheduled handler right away, so you can see it work.

What I use it for

Cron Triggers are my go-to for the quiet background chores: rolling up analytics overnight, pruning old data, checking if a site is up, sending a daily digest.

It’s the simplest way to run code on a schedule without owning a server. The full reference is in the Cron Triggers docs.

~~~

Related posts about cloudflare: