Free Cron Expression Parser

How this tool computes its result

Splits the expression into exactly 5 whitespace-separated fields (minute, hour, day-of-month, month, day-of-week). Each field is parsed independently: comma-separated parts, each of which may be a wildcard (*), a single value, a range (start-end), and/or a /step suffix. Ranges expand to a full array of candidate values, and a step keeps only the values whose position in that array is divisible by the step — which is mathematically equivalent to standard cron step semantics even for ranges not starting at 0. Month and weekday fields accept 3-letter aliases (jan-dec, sun-sat) and weekday 7 is normalized to 0 (Sunday). To preview upcoming runs, getNextRuns walks forward minute-by-minute from one minute after the reference time, checking all 5 parsed field sets against each candidate Date, up to a hard cap of 525,600 iterations (one year of minutes).

Worked example

Expression '0 9 * * 1-5' parses to minute={0}, hour={9}, dayOfMonth=1..31 (wildcard), month=1..12 (wildcard), dayOfWeek={1,2,3,4,5} (Mon-Fri). With the reference date/time set to a Friday afternoon, getNextRuns steps forward minute by minute and returns the next 8 matching timestamps — the next weekday at 9:00 AM, then each subsequent weekday at 9:00 AM, skipping Saturday and Sunday entirely.

When not to use this tool

There is no support for 6-field cron syntax with seconds, nor for special characters like L (last day), W (weekday nearest), or # (nth weekday of month) used by some schedulers (e.g. Quartz). If an expression can never match within the next year (for example day-of-month 31 combined with month February only), the preview silently returns fewer than 8 results after exhausting the 525,600-iteration guard rather than reporting that the schedule is unreachable.

Common mistakes

• - Pasting a 6-field cron string that includes a seconds field — parseCron requires exactly 5 fields and throws 'Cron expression must contain exactly 5 fields' otherwise.
• - Using a step of 0 or a negative step (e.g. '*/0') — explicitly rejected with an 'Invalid step' error rather than silently treated as 'every value'.
• - Entering an out-of-range value, like hour 25 or day 32 — parseNumber checks against each field's min/max and throws an explicit out-of-range error instead of clamping or wrapping.

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