chaitanya.dev / Tools / Cron Expression Explainer

Cron Expression Explainer

Paste a cron expression and get a plain-English description plus the next five firings. Zero dependencies, runs in your browser.

What does this cron actually mean?

Cron syntax is the kind of thing you read three times and still re-check. Paste a five-field expression below and get both a human summary and the next five actual firings, computed in your local time zone. No libraries, no network calls.

Notes

  • Five-field standard cron only. Six-field variants (Quartz’s seconds field, AWS EventBridge’s year field) and the 7-field k8s-style are not parsed here. Most Linux crontabs, GitHub Actions, and Vercel/Netlify cron functions use the five-field form.
  • Day-of-month and day-of-week both restrict. If you set both, a firing needs to match both — which is rarely what you want. The standard Vixie cron behaviour uses OR when either is *; this tool uses AND throughout (stricter, but predictable). If your real cron uses Vixie OR semantics, trust the next-firings list only when one of those two fields is *.
  • Time zone: firings are shown in the browser’s local time zone. Production crons typically run in UTC — double-check before copying times into an incident comms channel.