AI Cron Expression Explainer
Plain-English cron explanation that catches the OR-not-AND gotcha.
5-field standard cron, or 6-7 field Quartz syntax — say which flavor if it's not standard.
Not a one-line paraphrase — the real logic, including when fields combine unexpectedly.
The single most common cron misunderstanding, flagged automatically whenever it applies.
Most cron decoders convert an expression into one plain sentence and stop there — accurate for simple cases, but they skip the single most common cron misunderstanding: when both day-of-month and day-of-week are restricted (neither is a bare `*`), standard cron treats them as OR, not AND. Given `0 0 1,15 * 3` as input, most people reading it for the first time assume it runs at midnight on the 1st or 15th only when that date happens to fall on a Wednesday. That's wrong. Because both the day-of-month field (`1,15`) and the day-of-week field (`3`, Wednesday) are restricted, cron ORs them together — the job actually runs at midnight on the 1st, the 15th, and every single Wednesday, which is a very different and much more frequent schedule than the AND-reading most people bring to it. This tool states that OR relationship explicitly whenever both fields are restricted, rather than leaving it as an implicit detail buried in a general explanation. It also distinguishes standard Unix cron from Quartz cron by name rather than assuming one dialect: Quartz adds a seconds field (6-7 fields total instead of 5) and supports special characters — `L` for last, `W` for nearest weekday, `#` for the nth weekday of a month — that standard cron simply doesn't recognize, so a Quartz expression pasted into a standard-cron mental model gets silently misread. It's built for anyone who has to read someone else's cron schedule and get the actual run condition right the first time — reviewing a deploy pipeline's schedule, debugging why a job ran on an unexpected day, or double-checking a schedule before it ships to production. One honest limitation: this explains what an expression means and how often it fires in general terms; for exact upcoming timestamps in a specific timezone, pair this with your scheduler's own dry-run or next-run preview. Built by EngraveOcean as part of a small, growing set of free AI developer utilities, alongside AI Regex Explainer and AI JSON Schema Explainer — no login, no daily cap.