validate-a-cron-expression

# validate-a-cron-expression ## When to use - Use before creating or changing recurring scheduled work. - Do not assume five-field and six-field cron dialects are equivalent. ## Preconditions - Record scheduler, version, dialect, time zone, desired windows, holidays, duration, concurrency, and missed-run policy. ## Procedure 1. Parse with the exact scheduler implementation. 2. Generate future runs across ordinary, month-end, leap, daylight-saving, and year boundaries. 3. Compare every generated run to stated operational intent. 4. Check time zone source, clock, inclusive ranges, day-field semantics, and special tokens. 5. Define overlap, concurrency, catch-up, missed, retry, and duplicate behavior. 6. Test in a safe environment and record the next expected runs. ## Failure plan - Use an explicit scheduler or calendar table when cron cannot express the rule safely. ## Worked example A 02:30 local job has no run during a daylight-saving jump, so the team chooses UTC plus a business-calendar guard. ## Done - A cron validation report records dialect, expression, time zone, generated runs, edge cases, and execution policy - Month-end, leap, daylight-saving, overlap, missed-run, duplicate, and scheduler-version checks verify timing