Parser for cron expressions POSIX 5-field (min hour dom mon dow) + aliases (@yearly, @monthly, @weekly, @daily, @hourly) + natural language explanation + weekly visualizer (7 days x 24 hours matrix) + next 20 runs list. Supports standard Unix + AWS EventBridge + GitHub Actions + Kubernetes CronJob syntax. Fully.
minute hour dayOfMonth month dayOfWeek. Range: minute 0-59, hour 0-23, day of month 1-31, month 1-12 (or JAN-DEC), day of week 0-6 (0=Sunday, or SUN-SAT). Operators: * (any), , (list: 1,3,5), - (range: 1-5), / (step: */15).
@yearly = 0 0 1 1 *, @monthly = 0 0 1 * *, @weekly = 0 0 * * 0, @daily = 0 0 * * *, @hourly = 0 * * * *. Non-standard but widespread (Unix, Vixie cron, AWS EventBridge).
Matrix 7 days (mon-sun) x 24 hours. Active cells highlighted in blue. For high-frequency cron (e.g. * * * * * every minute) the matrix is fully blue.
List of the next 20 runs starting now. Useful to validate at a glance: '0 9 * * 1-5' = every weekday at 9:00, the times in the list confirm the pattern.
POSIX 5-field syntax. Unix standard since 1976 (V7). 5 space-separated fields: minute, hour, day of month, month, day of week. Operators: * (any value), , (value list), - (inclusive range), / (step). Example: */15 9-17 * * 1-5 = every 15 minutes from 9 to 17, mon-fri.
Differences across dialects. POSIX standard (Vixie cron Linux) uses 5 fields. AWS EventBridge uses 6 fields (adds optional year). Quartz Java uses 6-7 fields (adds seconds and year). The parser handles the standard 5-field case. For AWS EventBridge: use ? in place of day of week or day of month (AWS mutual exclusion).
Aliases. Vixie cron (Linux standard) supports non-POSIX aliases: @yearly / @annually / @monthly / @weekly / @daily (alias of @midnight) / @hourly / @reboot (runs at system startup, NOT handled by parser because it has no temporal schedule). The parser expands aliases internally before computation.
Scope caveat. The parser computes next runs based on browser clock (local timezone). For production cron with different timezone (e.g. UTC server but cron in Europe/Rome): next runs shown by the tool may be offset. For rigorous debugging: crontab -l on the actual server and cron-utils in Java/croniter in Python with explicit timezone.
| Cron | Meaning |
|---|---|
0 0 * * * | Every day at midnight |
0 9 * * 1-5 | Every weekday at 9:00 |
*/15 * * * * | Every 15 minutes |
0 */2 * * * | Every 2 hours (at minute 0) |
0 0 1 * * | First day of every month at midnight |
0 0 1 1 * | New Year's Day at midnight |
30 6 * * 0 | Sunday at 6:30 |
@daily | Every day at midnight (alias) |
@hourly | Every hour at minute 0 |
Technical terms used on this page, briefly explained.
crontab -e to edit, crontab -l to list. Syntax: one line per job, 5-field format + command. ? for mutual exclusion between dayOfMonth and dayOfWeek. / for regular repetition. */15 = every 15 starting from 0 (0, 15, 30, 45). 5/10 = every 10 starting from 5 (5, 15, 25...). 15,45 * * * * = at minutes 15 and 45 of every hour. The step */30 would start from 0, 30 - not from 15. For specific offsets: explicit list.while true; do...; sleep 30; done. AWS Step Functions / Cloud Scheduler GCP support sub-minute with different syntax.@reboot runs the job once at cron daemon startup (typically system boot), then never again until the next reboot. NO recurring temporal scheduling. The parser doesn't compute 'next run' for @reboot because it depends on when the machine restarts.schedule: - cron: '0 6 * * 1'. Caveat: GitHub Actions cron has +-5 minute precision for fairness, and jobs can be skipped during high scheduler utilization. For strict timing: use workflow_dispatch or webhook.0 9 1-7 * 1 = every Monday of the first week of the month (i.e. the first Monday). Works because in the first 7 days of the month exactly one Monday falls. Quartz cron supports 1#1 = first Monday natively, POSIX doesn't.CRON_TZ=Europe/Rome in crontab) and compute locally with that TZ.Maurizio Fonte, senior IT consultant with 20+ years in PHP, Laravel, unmanaged Linux infrastructure, applied cybersecurity and AI/LLM integration. Production backends, legacy code modernization, security audits, custom AI agents and MCP servers: the work behind every tool published here.
About Maurizio Fonte