Cron Expression Explainer
Read a cron expression in plain English and see exactly when it will next run.
How to use this tool
- Fill in the options above.
- The result updates as you change the input — there is nothing to submit and nothing to wait for.
- Read the figures in the result panel.
- Use Copy or Download if you need the output elsewhere. Nothing was uploaded at any point.
The next run times are calculated the way cron actually behaves, including the rule that trips up most implementations: when both the day-of-month and day-of-week fields are restricted, cron runs when <em>either</em> matches, not both. Expressions that can never fire, such as 31 February, are reported as such rather than hanging.
Cron Expression Explainer — the specification
| Input | Standard five-field cron expressions |
|---|---|
| Names | jan–dec and sun–sat accepted as well as numbers |
| Explains | Plain English description of the schedule |
| Predicts | Up to 20 upcoming run times in your local timezone |
| Errors | Named field and reason, not just "invalid" |
How it works
This tool runs entirely in your browser. There is no server involved, which means nothing you type or upload is transmitted, stored, or logged — and there are no usage limits, because there is nothing for us to ration.
You can confirm it yourself: open your browser's developer tools, select the Network tab, and use the tool. No request is made.
Who needs Cron Expression Explainer
Checking a crontab line before deploying it, working out why a scheduled job fires more often than expected, and confirming a CI schedule does what its author intended.
Cron Expression Explainer — frequently asked questions
What does "0 9 * * 1-5" mean?
At 09:00, every weekday. The fields are minute, hour, day of month, month and day of week, so this is minute 0 of hour 9 on days 1 to 5 of the week.
Why does my job run more often than I expected?
Most often the day-of-month and day-of-week trap. If both fields are restricted, cron fires when either one matches. "0 0 13 * 5" runs on every 13th and on every Friday, not only on Friday the 13th.
Which timezone are the predicted times in?
Your device’s local timezone. A server usually runs on UTC, so compare carefully before assuming the times match what will happen in production.
Does it support @daily or six-field expressions?
Not yet. This reads standard five-field cron. Six-field forms with seconds, and the @-shortcuts, are extensions that differ between implementations.
Does this work offline?
Yes. Once the page has loaded you can disconnect from the internet and it keeps working, because all the processing happens in your browser. That is also the simplest way to confirm nothing is being sent anywhere.
Is there a limit on how much I can paste in?
Nothing we impose. The practical limit is your device’s memory, since the work happens locally. Very large inputs get slower rather than being refused.
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