What cron actually is

Anatomy of a cron expression

Field ranges and allowed values

Special characters

* — every

, — list

- — range

/ — step

? — no specific value

Real examples

Common mistakes

Confusing day-of-week numbering

Forgetting timezone

Thinking */5 means "every 5 minutes starting now"

Using both day-of-month and day-of-week

Platform-specific variations

Shorthand expressions

How to read an unfamiliar expression

Try it without deploying anything

Free Online Cron Expression Builder — DevCrate Cron is one of those tools that every developer encounters eventually. You need to run a database backup every night, send a weekly digest email, or poll an API every five minutes — and someone mentions cron. You look up the syntax, copy something from Stack Overflow, it works, and you move on. Then six months later you need to change the schedule and you're staring at five numbers wondering what each one means again. This guide is meant to be the one you save. After reading it you should be able to read and write any cron expression from scratch, without guessing. Cron is a time-based job scheduler built into Unix-like operating systems. A cron job is a command or script that cron runs automatically on a defined schedule. The schedule is defined by a cron expression — a string of five fields that describe when to run the job. Cron expressions show up everywhere: Linux crontabs, GitHub Actions schedules, AWS EventBridge, Kubernetes CronJobs, Vercel cron functions, Railway cron jobs, and more. The syntax is largely the same across all of them, with minor variations. A standard cron expression has five fields separated by spaces: A helpful mnemonic: M H D M W — Minutes, Hours, Days, Months, Weekdays. An asterisk means "every valid value for this field." * in the minute field means every minute. * in the hour field means every hour. A comma lets you specify multiple values. 1,15,30 in the minute field means at minute 1, 15, and 30. A hyphen defines a range. 9-17 in the hour field means every hour from 9am to 5pm inclusive. A slash defines a step interval. */5 in the minute field means every 5 minutes. 0-30/10 means every 10 minutes between minute 0 and minute 30. Used in day-of-month and day-of-week fields to mean "I don't care." When you specify a day of week, use ? in the day-of-month field, and vice versa. Not all cron implementations support this — standard Linux crontab uses * instead. Different systems handle Sunday differently. In standard crontab, Sunday is both 0 and 7. In some systems, 0 is Sunday and 6 is Saturday. In others, 1 is Monday and 7 is Sunday. Always check the documentation for the platform you're using. When in doubt, use the three-letter abbreviation (SUN, MON, etc.) if the platform supports it — it's unambiguous. Cron runs in the timezone of the server unless configured otherwise. If your server is UTC and your users are in EST, a job scheduled for 0 9 * * * runs at 4am local time for East Coast users. Always be explicit about timezone. Most modern platforms (GitHub Actions, AWS, Vercel) let you specify timezone separately. */5 in the minute field means at minutes 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, and 55 — fixed to the clock, not relative to when the job was added. If you add a job at 2:03pm with */5, it first runs at 2:05pm, not 2:08pm. If you specify a value in both the day-of-month and day-of-week fields (rather than using * in one), most cron implementations treat them as an OR condition, not AND. 0 0 1 * 1 runs at midnight on the 1st of every month and every Monday — not just on Mondays that fall on the 1st. If you want "the first Monday of the month" you need a workaround, since standard cron can't express that directly. Standard Linux crontab uses the five-field format above. But many platforms extend or modify it: Many cron implementations support named shortcuts for common schedules: When you encounter a cron expression you don't immediately recognize, read it field by field left to right: minute, hour, day-of-month, month, day-of-week. Ask yourself: is this field a specific value, a range, a list, a step, or a wildcard? Build up the meaning piece by piece. Take 0 */6 * * *. Minute is 0 — on the hour. Hour is */6 — every 6 hours (0, 6, 12, 18). Day, month, and day-of-week are all wildcards. So: at midnight, 6am, noon, and 6pm, every day. Take 30 8 * * 1. Minute 30, hour 8, day-of-month wildcard, month wildcard, day-of-week 1 (Monday). So: 8:30am every Monday. I built the DevCrate cron builder because I found myself testing expressions by deploying jobs and watching logs — which is a slow, painful way to verify a schedule. The tool lets you paste any expression and instantly see the next several run times in plain English, without deploying anything. It also works the other way: pick a schedule from the visual builder and it generates the expression for you. Free, runs entirely in your browser, nothing to sign up for. Build and validate cron expressions with a visual editor. See human-readable output and next 10 run times instantly. Templates let you quickly answer FAQs or store snippets for re-use. Are you sure you want to ? It will become hidden in your post, but will still be visible via the comment's permalink. Hide child comments as well For further actions, you may consider blocking this person and/or reporting abuse