Cron Expression Parser

Cron Expression Parser decodes standard 5-field crontab expressions (minute, hour, day-of-month, month, day-of-week) into a plain-English sentence and a field-by-field breakdown. Paste something like "*/15 9-17 * * 1-5" and immediately see that it fires every 15th minute past hours 9 through 17, Monday through Friday - no more counting asterisks or second-guessing whether the third field is the day or the month.

Beyond translation, the tool computes the next five run times in both your local timezone and UTC. This matters more than it sounds: a huge class of production incidents comes from cron jobs that were scheduled against the wrong timezone or that silently never fire because day-of-month and day-of-week interact in the OR-semantics way Vixie cron defines. Seeing concrete upcoming timestamps is the fastest sanity check before you commit a schedule to a crontab, a Kubernetes CronJob, a GitHub Actions workflow, or an AWS EventBridge rule.

Everything runs 100% client-side in your browser - the expressions you paste never touch a server, which means it is safe to use with schedules from internal infrastructure, CI/CD pipelines, or anything else you would rather not paste into a random website. The parser supports the full standard syntax: wildcards (*), lists (1,15,30), ranges (1-5), step values (*/15, 1-10/2), and named months and weekdays (JAN-DEC, SUN-SAT).

One rule in cron catches almost everyone, and it is worth reading the breakdown for. When both day-of-month and day-of-week are restricted, cron runs the job when either matches, not when both do. So 0 0 1 * 1 fires on the first of the month and on every Monday, which is rarely what the author intended. The other regular surprise is daylight saving: a job scheduled inside the hour that a clock jumps forward does not run that day, and one inside the hour that repeats can run twice, because cron reads local time. Standard five-field cron has no seconds field, and @reboot is an event rather than a schedule, so neither can be previewed as a list of future times.

A two-line test shows what this cron expression parser checks. Enter 30 8 * * MON-FRI and click Parse: the Human-readable schedule reads "At 08:30, on Monday, Tuesday, Wednesday, Thursday, and Friday", the field table lists 30 for minute and 8 for hour, and the next five run times skip Saturday and Sunday. Now enter 0 9 * * 1-7. It is rejected with "Range "1-7" in day-of-week field is reversed (1 > 0)", because 7 is read as Sunday, which is 0. Write it as 0 9 * * * or 0 9 * * 0-6 instead.