Skip to content
Toolars
Explore

Cron Builder & Explainer

Build and explain five-field Cron; preview runs in UTC, your local zone or eight IANA zones, including DST cases. Five fields: minute, hour, day, month, weekday. Use decimal numbers, ascending ranges, lists and positive steps; 5/15 means 5 through the field maximum in steps of 15. Weekday 0/7 is Sunday. No seconds/year, ?, L, W, #, macros or commands. Limit: 512 UTF-8 bytes. Preview checks each UTC minute strictly after the browser's calculation time, for 366 days. Missing local minutes are skipped; repeated matching minutes appear twice. Browser time-zone data and actual scheduler DST/catch-up policies may differ. This does not execute jobs.

Task path / input to outcome

Enter the expression

Report bug

Local processing

Processing details

Tool inputs are processed on your device.

Resources may be downloaded to run this tool. Account services are separate.

Preparing offline use…

Privacy information

Task path / input to outcome

How to build and explain a cron schedule

  1. 01

    Enter the expression

    Weekday 0/7 is Sunday. Limit: 512 UTF-8 bytes.

  2. 02

    Choose the schedule zone

    This does not execute jobs.

  3. 03

    Calculate the schedule

    Choose Calculate schedule to validate the expression and preview upcoming minutes. Cancel calculation terminates the work, keeps your input and turns off auto-convert.

  4. 04

    Read the field explanations

    Each field shows its original expression followed by the exact sorted matching values. Steps reset within each field; they are not elapsed-time intervals. Weekday 7 is expanded before being normalized to Sunday 0. A day field begins with *: both day fields must match, including their steps. Neither day field begins with *: either day field may match.

  5. 05

    Verify the next runs

    Read the runs first, followed by the expanded fields and matching rule. The report includes its starting instant and inclusive search limit. Copy or download the same text; a partial result states how many of the requested runs were found.

Tool facts

Processing
In your browser
Input leaves this device
Never
Retention
Nothing is stored
Price
Free

Your input stays in the browser.

Cron Builder & Explainer uses its verified local execution path and does not create a hidden input or output history.

Local execution

Runs inside the current browser tab.

No hidden processing

Active tool data never becomes a Toolars document record.

No account required

Use the core workflow without creating a profile. Favorites sync to your account after you sign in.

Immediate reset

Clear the tab and the active working data is gone.

What Cron Builder & Explainer actually does

A backup job must fire at 02:30 on weekdays while the office sleeps; a report generator needs to run every 15 minutes starting at minute 5; a scheduler UI asks for a cron string and the team argues about what 0 9 1 * MON actually means — the first of the month, Mondays, or both. Cron Builder & Explainer settles it: paste the five fields and the explanation lists the exact matching values for each one, spelling out the day-field rule that 0 9 1 * MON fires when either condition matches, while 0 9 */2 * MON requires both. The next-runs preview checks each UTC minute for up to a year, skips minutes that DST removes, and shows repeated minutes twice, so the spring-forward gap can never be mistaken for a silent failure. Use it to draft a schedule before it ever touches crontab, systemd timers, or a cloud scheduler, and to decode a legacy expression nobody dares edit. Everything is computed in the browser, so production schedules and maintenance windows stay unpublished.

Common questions

Which cron syntax is supported?
Weekday 0/7 is Sunday. Limit: 512 UTF-8 bytes.
What happens when both day fields are set?
A day field begins with *: both day fields must match, including their steps.
Why does my expression fail to calculate?
The calculator found no matching minute within its search window of 366 days. That does not always mean the expression is wrong: a rare but valid schedule, such as one pinned to February 29, can fall outside the window. When some but not all requested runs are found, the report says how many — a partial result, not an invalid expression. Check that steps and ranges really cover the months and weekdays you intended.
What do the explanation lines mean?
Each field shows its original expression followed by the exact sorted matching values.
How does the next-runs list handle DST?
This does not execute jobs.
Is my schedule sent to a server?
No. Validation, explanation, and the next-runs calculation run in an isolated Worker inside this tab, the expression is never sent or retained, and no account is required.

Keep reading

Guides

Related tasks, not a dead end.

Move into another focused workspace without returning to the full index.

URL Workbench

Clean URL lists with signed-link protection and per-line reasons. Compare components and export sitemaps.

Edit

JSON Explorer

Query JSONPath, extract fields and round-trip JSON Pointer records without losing large-number precision.

Inspect

JSON Schema Validator

Validate Draft 7 or 2020-12 locally with exact error paths; infer schemas from multiple observed samples.

Inspect

HTML Publishing

Clean pasted HTML for publishing while preserving lists, links and table semantics; preview changes safely.

Publish