Cron to AWS EventBridge

Converting Unix cron to EventBridge

AWS EventBridge (and the older CloudWatch Events) uses its own cron dialect that is not quite standard Unix cron. This converter maps a familiar five-field expression onto the six-field EventBridge form and handles the quirks, so a schedule that works on a Linux box translates correctly into a scheduled rule.

When you reach for it

You use it when moving a scheduled job from a server crontab to a serverless Lambda trigger, when an EventBridge rule rejects an expression you copied from Unix cron, or when you want to confirm the AWS form before wiring it into infrastructure code.

Example

# Unix cron: 30 6 * * 1-5 (06:30 Mon-Fri)
# EventBridge wants six fields and UTC:
cron(30 6 ? * MON-FRI *)

Note the extra year field at the end and the ? where Unix would write * for day-of-month.

Common pitfalls

The defining difference is the six fields: EventBridge adds a year field that Unix cron lacks, so a five-field expression is simply invalid. Worse, EventBridge forbids specifying both day-of-month and day-of-week at once, exactly the opposite of Unix flexibility. One of the two must be a ? (meaning no specific value) while the other carries the rule. Writing * in both day fields is rejected. The last trap is time zone: EventBridge cron expressions are evaluated in UTC, so a 6am local job must be offset to the matching UTC hour. Validate the underlying schedule with the next-run calculator first.

FAQ

Why is my five-field expression rejected? EventBridge requires six fields including year. Add the trailing year field, usually *.

What is the ? for? It means "no specific value" and must be used in exactly one of the day fields, since you cannot specify both.

Does EventBridge use my local time? No, cron expressions run in UTC. Convert your local hour to UTC before entering it.