How to build a cron expression
Compose a 5-field cron schedule (minute, hour, day, month, weekday) and see it explained in English.
Builder vs explainer
Cron Builder helps you write an expression from fields. Cron Explainer does the reverse: paste an existing expression and read it in plain English.
Steps
1) Open Cron Builder. 2) Use Builder dropdowns or a preset (Weekdays at 9 AM is a common start). 3) Read the 5-field expression, the English summary, and next run times — they update as you change fields. There is no Run button on the article page. 4) Switch to Editor to type a string. Example: 0 9 * * 1-5 is 09:00 Monday–Friday. Seconds (six-field) are not supported. Confirm UTC vs local against the system that will run the job. Use Cron Explainer if you already have a crontab string.
Limits
This is UNIX-style five-field cron, not systemd OnCalendar and not GitHub Actions weekday numbering. ? on day fields is treated like *. Next-run times are computed in this browser. Nothing is uploaded. Cron Explainer at /tools/cron-explainer is the paste-a-string sibling — the dedicated how-to covers reading expressions in English. Quartz seven-field and AWS cron extras will not mean what you think. Confirm the daemon timezone (often UTC) against the next-run table, which uses this browser. Related: /guides/how-to-explain-cron-expressions and /tools/timestamp-converter if you were looking at Unix seconds instead of a crontab.