Cron Explainer

Cron is a time-based job scheduler built into Unix-like operating systems. It runs commands or scripts automatically at specified times and intervals. A crontab (cron table) file contains a list of cron expressions, each defining exactly when a job should run, from once a year to every minute. Cron powers everything from nightly database backups and weekly report emails to hourly cache-clearing jobs and real-time health checks that run every minute.

A standard cron expression has five fields separated by spaces: minute (0–59), hour (0–23), day of month (1–31), month (1–12), and day of week (0–7, where both 0 and 7 represent Sunday). Special characters add flexibility: `*` means "every", `/` means "every N" (so `*/15` in the minute field means every 15 minutes), `-` defines a range (`9-17` means 9am through 5pm), and `,` lists multiple values (`1,3,5` means Monday, Wednesday, Friday).

Reading cron expressions from memory is a skill that takes practice. `0 3 * * 1` (runs at 3am every Monday) looks cryptic until you memorise the field order. Even experienced developers look up "what does this cron do?" regularly. This tool decodes any cron expression into a plain English description ("Every Monday at 3:00 AM") and shows the next 5 scheduled run times in your local timezone, so you can immediately verify whether the schedule matches your intent.

A growing library of common pre-set expressions lets you start from a working template and adjust from there.