Cron Expression Cheat Sheet: Every Syntax Pattern with Examples

Understanding Cron Syntax

A cron expression is a string of five (or six) fields that defines when a scheduled job runs. Each field represents a unit of time, and together they form a precise schedule that repeats automatically.

The standard five-field format:

┌───────────── minute (0–59)
│ ┌───────────── hour (0–23)
│ │ ┌───────────── day of month (1–31)
│ │ │ ┌───────────── month (1–12)
│ │ │ │ ┌───────────── day of week (0–7, where 0 and 7 are Sunday)
│ │ │ │ │
* * * * *

Some systems (like AWS EventBridge, Quartz Scheduler) add a seconds field before the minute, making it six fields total.

Special Characters Explained

The Most Common Cron Schedules

These are the patterns developers reach for most often:

Every Minute

* * * * *

Rarely used in production. Avoid this for anything with meaningful I/O — it runs 1,440 times a day.

Every 5 Minutes

*/5 * * * *

The most common schedule for health checks, polling tasks, and lightweight background jobs.

Every 15 Minutes

*/15 * * * *

Good for syncing data or checking for updates without overwhelming a service.

Every Hour (at the top)

0 * * * *

Runs at minute 0 of every hour: 1:00, 2:00, 3:00...

Every Hour (at a specific minute)

30 * * * *

Runs at minute 30 of every hour: 1:30, 2:30, 3:30... Useful to offset from the top of the hour when servers are busy.

Once a Day at Midnight

0 0 * * *

Daily cleanup jobs, report generation, cache invalidation.

Once a Day at 2 AM

0 2 * * *

Database backups, log rotation — scheduled during off-peak hours.

Every Day at 8 AM and 6 PM

0 8,18 * * *

Twice-daily summaries or digest emails.

Every Weekday at 9 AM

0 9 * * 1-5

Business-hours-only jobs: send morning reports, sync calendars.

Every Monday at Midnight

0 0 * * 1

Weekly tasks: generate weekly summaries, clean up old sessions.

First Day of Every Month

0 0 1 * *

Monthly billing cycles, subscription renewals, report generation.

Last Day of Every Month

0 0 L * *

Note: L is supported in Quartz and some extended cron parsers, but not standard Unix crontab. For standard cron, use a script that checks the date.

Complete Reference Table

Cron in Different Environments

The base syntax is the same, but each platform has quirks.

Linux / Unix crontab

# Edit your crontab
crontab -e

# View current crontab
crontab -l

# System-wide crontabs live in /etc/cron.d/
# Each line: minute hour day month weekday user command
*/5 * * * * deploy /usr/bin/python3 /opt/scripts/check.py

GitHub Actions

on:
  schedule:
    - cron: '0 9 * * 1-5'  # Weekdays at 9 AM UTC

GitHub Actions uses UTC. The minimum interval is every 5 minutes, and jobs may be delayed during heavy load.

AWS EventBridge (CloudWatch Events)

AWS uses a six-field format with seconds first, and minutes second:

cron(0 12 * * ? *)   # Every day at noon UTC
cron(0/5 * * * ? *)  # Every 5 minutes

Note: AWS uses ? in place of * for day-of-month or day-of-week when the other is specified.

Node.js (node-cron)

const cron = require('node-cron');

// Every 5 minutes
cron.schedule('*/5 * * * *', () => {
  console.log('Running task every 5 minutes');
});

// Every weekday at 9 AM
cron.schedule('0 9 * * 1-5', () => {
  sendMorningReport();
});

Python (APScheduler)

from apscheduler.schedulers.blocking import BlockingScheduler

scheduler = BlockingScheduler()

@scheduler.scheduled_job('cron', hour=9, minute=0, day_of_week='mon-fri')
def send_daily_report():
    print('Sending report...')

scheduler.start()

Common Mistakes

Not using UTC — Most cron systems run in UTC. A job at "midnight" may fire at noon your time. Always check which timezone your scheduler uses and document it explicitly.

Using * in every field — * * * * * fires every minute. If your job takes more than 60 seconds to run, overlapping executions will pile up. Add locking or use */5 at minimum.

Day-of-month and day-of-week interactions — In standard cron, if both are set (not *), the job runs when either condition is true, not both. This is the source of many unexpected extra runs. Use ? in systems that support it to explicitly say "I don't care about this field."

No error alerting — A failed cron job often fails silently. Always redirect stderr to a log file and set up monitoring or alerting for failed runs.

# Capture both stdout and stderr
*/5 * * * * /opt/script.sh >> /var/log/script.log 2>&1

FAQ

How do I run a cron job every 2 hours starting at midnight? 0 */2 * * * — This runs at 0:00, 2:00, 4:00, ... 22:00.

How do I run a cron job at 9:30 AM and 3:30 PM? 30 9,15 * * *

Can a cron expression run on the last weekday of the month? Not in standard cron. You need a script that calculates this, or use an extended scheduler like Quartz.

What's the smallest interval cron supports? Standard cron supports down to every minute (* * * * *). For sub-minute intervals, use a process manager, a message queue, or a scheduler that supports seconds.

→ Use the Crontab Generator to build and validate any cron expression visually — no syntax memorization needed.