What does `0 0 * * 0` mean?

At 00:00 on Sunday. Reading the fields in order: minute, hour, day of month, month, day of week.

What time zone will this run in?

System local time under standard crontab, but UTC on Vercel, GitHub Actions, Kubernetes and AWS EventBridge. Convert before deploying — and remember that a conversion crossing midnight also shifts the day fields.

How do I test a cron expression without waiting?

Preview the next run times, as the tool above does, and run the job manually first. Never validate a schedule by waiting for it to fire in production — you learn about the mistake a day late.

Cron Every Week

`0 0 * * 0`

At 00:00 on Sunday

Field by Field

Field	Value	Matches
Minute	`0`	0
Hour	`0`	0
Day of month	`*`	every day
Month	`*`	every month
Day of week	`0`	0

Which Day Is the Week?

@weekly is Sunday at midnight, which surprises teams whose week starts on Monday. Be explicit:

Expression	Runs
`0 0 * * 0`	Sunday at midnight
`0 0 * * 1`	Monday at midnight
`0 9 * * 1`	Monday at 9am — before the week starts
`0 17 * * 5`	Friday at 5pm — weekly summary

Weekly Jobs Fail Quietly

A job that runs 52 times a year gets 52 chances to be noticed and one chance a week to be missed. Alert on *absence*: if the weekly report has not landed by Monday lunchtime, something should page, because nobody notices a missing email.

Time Zones

Standard crontab evaluates in system local time. Vercel Cron, GitHub Actions, Kubernetes CronJobs and AWS EventBridge all evaluate in UTC. If converting your local time crosses midnight, the day-of-week field shifts too — weekdays at 5pm in UTC-07:00 is 0 0 * * 2-6, not 0 0 * * 1-5.

The Day-Field Trap

When both the day-of-month and day-of-week fields are restricted, cron matches either, not both. 0 0 13 * 5 runs on every 13th *and* every Friday — not Friday the 13th. Leave one of them as * unless you genuinely want the union.

Other Common Schedules

Expression	Runs
`* * * * *`	Every minute
`/5 * * *`	Every 5 minutes
`/15 * * *`	Every 15 minutes
`0 * * * *`	Every hour, on the hour
`0 0 * * *`	Every day at midnight
`0 9 * * *`	Every day at 9am
`0 9 * * 1-5`	Weekdays at 9am
`0 9 * * 1`	Every Monday at 9am

Making the Job Safe

Assume double firing. DST transitions, restarts and retries all cause it. Make the job

idempotent rather than assuming exactly-once.

Assume overlap. Cron starts the next run whether or not the last one finished. Take a

lock.

Avoid :00. Every hourly job on the internet fires at the top of the hour; a random

minute spreads load on shared APIs.

Log the start and end. A cron job that silently stops running is invisible until

someone notices the missing output.

Deploying This Schedule

``bash # crontab -e (system local time) 0 0 * * 0 /usr/local/bin/job.sh >> /var/log/job.log 2>&1`

`json // vercel.json (UTC) { "crons": [{ "path": "/api/job", "schedule": "0 0 * * 0" }] }`

`yaml # .github/workflows/job.yml (UTC) on: schedule: - cron: '0 0 * * 0'`

Starting from midnight UTC on 1 January 2026, this fires at:

Next runs
2026-01-04 00:00 UTC
2026-01-11 00:00 UTC
2026-01-18 00:00 UTC
2026-01-25 00:00 UTC


At 00:00 on Sunday.

`Making It Survive Production`

Redirect output. A cron job with no redirect emails its output to the crontab owner,

  and on most servers that mail goes nowhere. Log to a file instead.

Use absolute paths. Cron runs with a minimal environment — no PATH you recognise,

no shell profile, no nvm

. A script that works in your terminal frequently fails here
  for exactly that reason.

Escape percent signs. In a crontab, % means newline. date +\%Y needs the

  backslash or the command truncates at the percent.

Take a lock. Cron starts the next run whether or not the last finished. flock` is

one line and prevents the overlap.

Alert on absence. A job that stops running is silent. Ping a dead-man's-switch service

on success so the *lack* of a ping is what pages you.