Cron Expression Generator

A Cron Expression is a string format used to define when scheduled tasks should run, originating from Unix/Linux crontab. It uses 6 or 7 fields (second, minute, hour, day, month, week, year) to precisely control task execution cycles.

The standard seven-field format is: sec min hour day mon week [year]. Each field supports wildcards *, ranges 1-5, intervals 0/15, lists 1,3,5, and special characters like ? (unspecified), L (last day), and W (nearest weekday).

Today Cron has been adopted by nearly every major scheduling framework including Java Quartz, Spring Schedule, and Node.js node-cron — making it the standard approach for configuring backend scheduled tasks.

Cron expressions seem simple but frequently cause production issues:

• Day-of-month vs Day-of-week conflict: Most implementations don't allow both to be specified with concrete values simultaneously; one must be set to ?.
• Week field standards vary: Linux crontab uses 0=Sunday or 7=Sunday; Spring uses 1=Sunday; Quartz supports SUN-SAT abbreviations. Use the top-right switch in this tool to change standards.
• 6-field vs 7-field: Traditional Linux crontab uses 5/6 fields (no seconds); Spring and Quartz support 7 fields (with seconds and year). Always verify target system format before copying.
• "Last day of month" gotchas: L in the day field means last day, but combined with W in some frameworks the semantics may differ.

This tool provides real-time preview of the next 7 execution times, helping you quickly spot these issues.

This tool's core design principle is "100% frontend-only operation." All Cron expression generation, parsing, and preview calculations happen locally in your browser. Your time rules and business data are never sent to any server, nor saved anywhere.

For expressions containing sensitive scheduling information (production backup windows, key rotation schedules, etc.), we recommend using the tool offline or in a controlled environment, or manually redacting critical details before pasting.