Cron expression parser

About this converter

Cron syntax is five or six fields of numbers and asterisks that encode a schedule, and almost nobody can read it confidently at a glance. The consequences of getting it wrong are asymmetric: a job that runs too rarely is a quiet bug you find weeks later, and one that runs every minute instead of every hour is an incident. Reading the schedule back in English before you commit it takes five seconds.

Paste one expression or a whole block of them, one per line, and each gets described. Lines starting with a hash are skipped, so you can paste a crontab straight from the server without editing it first. Trailing commands are ignored too, which means a real crontab line with a schedule followed by the command it runs is parsed correctly rather than rejected.

Both common dialects work. Standard crontab uses five fields - minute, hour, day of month, month, day of week. Quartz and Spring add a seconds field at the front, making six. The parser detects which you have pasted rather than making you declare it.

The day-of-week option exists because this is the field implementations disagree about most. Standard cron numbers Sunday as 0; Quartz numbers Sunday as 1, shifting every day by one. A schedule you believe runs on Friday may run on Saturday if you assumed the wrong convention. Set the option to match your scheduler and check the description says the day you expect.

Expressions that fail to parse report an error on that line rather than failing the whole batch, so pasting a full crontab tells you which entries are wrong.

Nothing is uploaded. Your crontab often reveals your entire backup and deployment schedule, which is not information worth handing to a random server.

Frequently asked questions

Five fields or six?

Standard crontab uses five. Quartz and Spring use six, with seconds at the front. The parser detects which you pasted.

My schedule runs on the wrong day. Why?

Almost certainly the day-of-week convention. Standard cron numbers Sunday as 0, Quartz numbers it as 1. Toggle the option and see which description matches your intent.

Can I paste a whole crontab?

Yes. Comments are skipped and trailing commands after the schedule are ignored, so a file copied from the server works as-is.