# Why IndieCrontab exists

> A valid cron expression can change meaning or fail when it moves between platforms.

By turushan.

Published: 2026-09-03T00:00:00.000Z

Updated: 2026-09-18T20:02:03Z

Canonical: https://indiecrontab.com/blog/why-indiecrontab-exists/

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](https://developers.cloudflare.com/workers/configuration/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](https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#onschedule)
accepts five-field POSIX syntax but will not schedule more often than every five minutes.
[Vercel](https://vercel.com/docs/cron-jobs) refuses named months and weekdays, and it does not let
both day fields carry values. Its [Hobby
rules](https://vercel.com/docs/cron-jobs/manage-cron-jobs#cron-jobs-accuracy) allow one run per day
and can choose any moment inside the requested hour. [AWS EventBridge
Scheduler](https://docs.aws.amazon.com/scheduler/latest/UserGuide/schedule-types.html) 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)](https://man7.org/linux/man-pages/man5/crontab.5.html), 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, cookie, or public list of expressions people checked.
Analytics is currently off, so no tracker receives the expression.

Read [UTC evaluation and the timezone display](https://indiecrontab.com/#what-timezone-does-cron-run-in). Use [IndieCrontab](https://indiecrontab.com/) to inspect an expression's next five UTC matches and platform compatibility notes.

## Sources

- https://man7.org/linux/man-pages/man5/crontab.5.html
- https://developers.cloudflare.com/workers/configuration/cron-triggers/
- https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#onschedule
- https://vercel.com/docs/cron-jobs
- https://vercel.com/docs/cron-jobs/manage-cron-jobs
- https://docs.aws.amazon.com/scheduler/latest/UserGuide/schedule-types.html