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5 fields · ranges · steps · live

Decode any cron expression

Paste a 5-field cron expression to see a plain-English description and the next 10 fire times. Parses ranges, steps, lists, and wildcards.

Quick Start

How to read a cron expression

Five space-separated fields: minute, hour, day-of-month, month, day-of-week. Use * for "any", */N for steps, A-B for ranges, A,B,C for lists.

  1. 01

    Paste expression

    Five fields separated by spaces. Use * for "every".

    Parsing accepts ISO 8601, RFC 3339, RFC 2822, and Unix epoch seconds/milliseconds. The Date constructor handles the rest with browser-engine consistency.

    inputISO 8601RFC 3339epochlive
    expr · timestamp5 · ISO
    */5 9-17 * * 1-5
    loaded · ISO 8601zone · ready
  2. 02

    Read description

    Plain English summary of when it will fire.

    All math runs in UTC internally to avoid DST landmines; presentation converts back to the user’s zone via Intl.DateTimeFormat.

    descUTC mathIntlDST-safelive
    desc · optionsen · live
    Every 5 minutes, 9am-5pm,
Monday–Friday
    options applied · UTCDST-safe
  3. 03

    Preview next 10 runs

    Concrete fire times to sanity-check schedules.

    Output respects the chosen timezone offset (Z vs +05:30) and pads digits per ISO conventions so sorts stay chronological.

    previewoffsetzone-awaresortablepadded
    next · computed10 · ready
    Mon 09:00:00
Mon 09:05:00
Mon 09:10:00
    computed · instantsortable
  4. 04

    Copy or download

    Grab the description + run list as text.

    Copy writes via the Async Clipboard API; nothing pings a time server — the browser’s clock is the only oracle.

    exportclipboardno oracledeterministicclient-side
    ok · copiedready · done
    Copied
    shipped · ready to shipsuccess
Pro tips

Time math without DST landmines

Always store UTC

Convert to local for display only. UTC storage avoids DST jumps and timezone drift in databases.

Watch leap seconds

POSIX time doesn’t count leap seconds; some systems do. Don’t use timestamps for sub-second precision across boundaries.

Prefer Temporal eventually

The Date API has many quirks. Temporal is shipping in modern engines and handles zones correctly.

Cron is timezone-tricky

Cron expressions run in the daemon’s local zone unless told otherwise. Pin a TZ explicitly for predictable runs.

ISO 8601 sorts naturally

YYYY-MM-DDTHH:mm:ss sorts correctly as a string. Don’t use US-style MM/DD/YYYY for anything machine-readable.

Beware Y2K38

Signed 32-bit Unix timestamps overflow in 2038. Use 64-bit storage end-to-end for long-lived systems.

Related toolsCron BuilderCron Next RunsRate Limit CalculatorTimezone ConverterDuration CalculatorTime Arithmetic
Use Cases

When to decode cron

Job audits, infra reviews, debugging cron failures.

Code review

Make sure the schedule in a PR matches the intent in the commit message. Math runs in UTC under the hood to dodge DST jumps — local time is only for display. That means scheduling logic and date diffs survive March / November fall-back without the classic off-by-one-hour bug.

DST-safe

Infra audits

Read a crontab without firing up a sandbox VM. Browser clock is the only source — no external time server, no privacy leak, no rate limit. Pair with NTP-synced server time for high-accuracy use cases, but for human-scale work the browser clock is plenty.

UTC-correct

On-call debugging

Confirm a missed run wasn't expected to skip. ISO 8601 output sorts naturally as strings, perfect for filenames (report-2026-01-15.pdf) and log lines that need chronological ordering without parsing. Drop into S3 keys for free time-bucketing.

ISO-sortable

Learning cron

Verify your understanding of */5 and 1-5,*/2 quirks. Pairs cleanly with cron, scheduled tasks, and timestamped log analysis. The tool's output drops directly into APScheduler, Linux cron, or GitHub Actions schedule expressions without re-formatting.

spec-grade

Cross-tool sync

Compare GitHub Actions cron with Kubernetes CronJob syntax. Output respects the chosen timezone offset (Z vs +05:30) so REST APIs and database TIMESTAMP WITH TIME ZONE columns round-trip cleanly. No ambiguity between "noon UTC" and "noon local".

zone-aware

Migrations

Document existing schedules before switching to a new scheduler. Confirms the difference between epoch seconds (10 digits) and milliseconds (13 digits) before you commit code that mis-multiplies by 1000 — a classic bug in cross-language time handling.

epoch-accurate
FAQ

Frequently asked questions

Standard 5-field cron only. Quartz / AWS EventBridge 6-7 field variants (seconds, year) aren't supported here.
Use the literal 0 0 * * * (daily) or 0 * * * * (hourly). Aliases vary by implementation; we expand the canonical form.
No — those are Quartz extensions. This parser sticks to POSIX cron.
0 = Sunday in most implementations; 7 also means Sunday for compatibility. Use 1-5 for weekdays.
No. Parsing runs locally in your browser.
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