Parse a cron expression and return a human-readable description of when it fires. Supports 5-field standard cron (min hour dom month dow) plus extensions: L (last day/weekday), W (nearest weekday), # (nth weekday), and named months/days (JAN..DEC, SUN..SAT). Use this to explain any cron schedule in plain English.

Deeply validate a cron expression for correctness and common mistakes. Catches: impossible schedules (e.g. day 31 in Feb), OR-semantics gotchas (dom AND dow both restricted = either matches, not both), midnight scheduling spikes, uneven step values (*/7), leap-year edge cases, weekday-only warnings, and more. Returns warnings, observations, optimization suggestions, and an estimated yearly run count. Use this BEFORE deploying a cron job to catch silent failures.

Compute the next N scheduled run times for a cron expression. Returns ISO-8601 timestamps with relative offsets (+5m, +1h, +2d). Use this to preview when a job will actually fire before committing it.

Return a library of common cron expression presets (every 5 min, hourly, daily at midnight, weekdays 9am, monthly, quarterly, yearly, etc.) with their plain-English labels. Use this when a user asks for a "common" or "standard" schedule and you want to offer proven starting points.