A cron expression can be valid and still travel badly.
Take 0 9 * * 1. A POSIX-style crontab reads weekday 1 as Monday. Cloudflare Cron
Triggers reads 1 as
Sunday. The same five fields can run on the wrong day without looking broken.
The other platforms add different boundaries. GitHub Actions accepts five-field POSIX syntax but will not schedule more often than every five minutes. Vercel refuses named months and weekdays, and it does not let both day fields carry values. Its Hobby rules allow one run per day and can choose any moment inside the requested hour. AWS EventBridge Scheduler expects a wrapped expression with a sixth year field.
IndieCrontab puts those differences beside the explanation. Paste one common five-field expression. The tool parses the grammar documented in crontab(5), writes its meaning in plain English, calculates the next five runs in UTC, translates those instants into your browser’s timezone, and links every platform verdict to the rule that produced it.
The preview deliberately uses UTC for one stable comparison. A local cron daemon can use another timezone. The platform table records what each vendor documented on 2026-09-03, and those rules can change.
The check stays private and free. There is no account, card, premium plan, analytics script, cookie, or public list of expressions people checked.