Cron expressions explained — a complete guide with real examples

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. What cron actually is 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,