Cron Expression Builder

The Cron Expression Builder is an interactive, visual tool for constructing cron schedule expressions. Cron expressions are five-field strings (minute hour day-of-month month day-of-week) used by Unix cron, systemd timers, GitHub Actions, GitLab CI, and many CI/CD platforms to define recurring schedules. The tool provides five labeled input fields — Minute (0-59), Hour (0-23), Day of Month (1-31), Month (1-12), and Day of Week (0-6, where 0 is Sunday) — each accepting standard cron syntax: asterisks for wildcards, specific values, ranges (1-5), steps (*/5), and lists (1,3,5). As you fill in each field, the tool assembles the complete cron expression in a monospace display below the inputs, and simultaneously generates a human-readable description of the schedule (e.g., "Runs at minute 0, at hour 9, on day-of-week 1-5" or "Runs every minute"). This immediate feedback eliminates the trial-and-error process of constructing cron expressions manually and the need to consult cron documentation for syntax questions.

Cron syntax is compact but non-obvious. A five-field string like "0 22 * * 1-5" requires mental parsing: minute 0, hour 22, every day of the month, every month, days 1-5 of the week — that is, "10 PM on weekdays". The Cron Expression Builder removes this mental overhead by providing real-time validation and translation. The human-readable description immediately confirms whether the expression matches your intent, catching mistakes before they cause missed scheduled runs or unexpected executions. Common use cases include setting up CI/CD pipelines, configuring scheduled tasks in crontab, defining GitHub Actions workflow triggers, scheduling database backups, and setting up periodic data synchronization jobs.

This tool runs entirely in your browser — no data ever leaves your device. There is no server round-trip, no upload, no logging, and no account required. Your input is processed locally using client-side JavaScript and is never stored, transmitted, or accessible to anyone else. When you close the tab, everything disappears.

Does this validate the cron expression?

<p>The tool assembles the expression from your inputs but does not perform deep validation of cron semantics (e.g., it will not warn that February 30 is impossible). The description serves as a semantic check — read it to confirm the schedule matches your intent.</p>

Can I use this with non-Unix cron systems?

<p>The five-field format is the standard Unix/POSIX cron syntax. Some systems (like GitHub Actions) use slightly different formats. The basic five fields are compatible with most systems, but check your platform's documentation for any additional fields or restrictions.</p>

What does day-of-week 0 mean?

<p>In standard cron, 0 is Sunday, 1 is Monday, ..., 6 is Saturday. Some systems use 7 for Sunday. The tool uses the 0=Sunday convention, which is the most widely supported.</p>