Crontab Explainer
Paste any cron expression and get a plain-English explanation, a field-by-field breakdown, and the next 10 scheduled run times. Supports the standard 5-field syntax used by Unix/Linux cron, AWS CloudWatch Events, GitHub Actions, Kubernetes CronJobs, and most scheduling systems.
Why Cron Is Hard to Read
Cron compresses a calendar's worth of meaning into five fields and a handful of operators. 0 9 * * 1-5 is every weekday at 9 AM. */15 * * * * is every 15 minutes. 0 0 1 */2 * is midnight on the 1st of every other month. The problem isn't that the rules are complicated — it's that they're so dense that even people who write cron expressions weekly will pause to second-guess one. Reading it back in English is faster than mentally re-parsing the punctuation.
The other reliable foot-gun is day-of-month and day-of-week interacting. In standard cron, if both fields are restricted (neither is *), the schedule fires when either condition matches — not both. 0 0 13 * 5 runs at midnight on the 13th and also every Friday, not just on Friday the 13th. The explainer surfaces this so you don't ship a calendar bug to production.
How It Works
The parser splits the expression on whitespace, validates each field against its allowed range, expands operators (* every, / step, - range, , list), and generates a human-language description. The next-run calculator walks forward from now in 1-minute increments, checking each candidate timestamp against every field, and stops at 10 matches. All timezone math uses the browser's local zone — if your server runs UTC and you're in PT, mentally offset by the difference, or temporarily change your system clock to verify.
Common Use Cases
Debugging a scheduled job that's firing at the wrong time. Reviewing a teammate's Terraform or Helm config before merging. Translating a cron one-liner from a curl command or shell script into something a non-engineer stakeholder can read. Sanity-checking a backup window before flipping the rollout. Or just refreshing your memory on whether * * * * * means every minute (it does).
How We Compare
Crontab.guru is the best-known explainer and a great tool — it's been the de facto cron Rosetta Stone for years. This tool covers the same standard 5-field grammar and adds inline links to the rest of the UDT toolkit so a cron line in a script flows into the related developer utilities. Both run in the browser; neither uploads. If your cron flavor uses six fields (seconds first) like Quartz or AWS EventBridge, those use extended syntaxes this tool doesn't handle — drop the seconds and the explainer covers the remaining five fields correctly.
Frequently Asked Questions
Built by Derek Giordano · Part of Ultimate Design Tools