Cron Expression Parser and Builder Tool - Schedule Generator with Next Run Times

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This tool parses and builds cron expressions used for scheduling recurring tasks. It supports both standard Unix cron (5-field) and AWS EventBridge/CloudWatch cron (6-field) syntax. Enter a cron expression to get a human-readable description and see the next scheduled execution times, or use the visual builder to construct expressions interactively.

All processing is performed entirely in your browser using client-side JavaScript. No data is transmitted to any server. Your cron expressions never leave your device.

  • This tool is provided "AS IS" without any warranties of any kind.
  • The author accepts no responsibility for incorrect schedule calculations or missed executions.
  • Always verify cron expressions in your target environment before deploying to production.
  • Next execution times are calculated based on your local system clock and timezone.
  • By using this tool, you accept full responsibility for any outcomes.

This tool uses client-side JavaScript for all processing. No data is transmitted to servers, no files are uploaded online, all processing happens locally in your browser. Once loaded, this tool continues to work even without an internet connection. For more details, please refer to our Web Tools Disclaimer.

Standard: minute hour day-of-month month day-of-week
AWS EventBridge: minute hour day-of-month month day-of-week year
FieldTypeValue
Minute
(0-59)
Hour
(0-23)
Day of Month
(1-31)
Month
(1-12)
Day of Week
(0-6, SUN=0)
Generated Cron Expression:
Human-Readable Description
Field Breakdown
Next Scheduled Executions

Features

  • Parse standard Unix cron expressions (5 fields: minute, hour, day-of-month, month, day-of-week)
  • Parse AWS EventBridge / CloudWatch cron expressions (6 fields, including year)
  • Generate human-readable descriptions of cron schedules
  • Calculate next N scheduled execution times (5, 10, 15, 20, or 25)
  • Visual cron expression builder with interactive field selectors
  • Support for special characters: * , - / ? L W #
  • Support for month names (JAN-DEC) and day-of-week names (SUN-SAT)
  • Preset common cron expressions for quick reference
  • Field-by-field breakdown table showing what each part of the expression means
  • Copy expressions and descriptions to clipboard
  • 100% client-side processing - no data sent to any server

How to Use

  1. Parse Mode: Enter a cron expression in the input field, select the syntax type (Standard Unix or AWS EventBridge), and click "Parse Expression" to see the description and next run times.
  2. Build Mode: Switch to the "Build Expression" tab. Select the type and values for each field (minute, hour, day-of-month, month, day-of-week, and optionally year for AWS). Click "Build Expression" to generate the cron string.
  3. Presets: Use the "Presets" dropdown to quickly load common cron expressions like "Every 5 minutes" or "Every weekday at 9:00 AM".
  4. Copy: Use the copy buttons to copy the expression or description to your clipboard.
  5. Parse Built Expression: After building an expression, click "Parse This Expression" to switch to Parse mode and see the full analysis.

Cron Syntax Reference

  • * — Any value (matches all)
  • , — List separator (e.g., 1,3,5)
  • - — Range (e.g., 1-5 means 1 through 5)
  • / — Step (e.g., */5 means every 5 units, 10/5 means starting at 10, every 5)
  • ? — No specific value (used in day-of-month or day-of-week to avoid conflicts)
  • L — Last (day-of-month: last day of month; day-of-week: last specific day, e.g., 5L = last Friday)
  • W — Nearest weekday (e.g., 15W = nearest weekday to the 15th)
  • LW — Last weekday of the month
  • # — Nth occurrence (e.g., 5#3 = third Friday of the month)

Important Notes

  • Standard Unix cron uses 5 fields: minute (0-59), hour (0-23), day-of-month (1-31), month (1-12), day-of-week (0-6 where 0=Sunday).
  • AWS EventBridge/CloudWatch cron adds a 6th year field (1970-2199) and requires ? in either day-of-month or day-of-week.
  • Month names (JAN, FEB, ...) and day-of-week names (SUN, MON, ...) can be used in place of numbers.
  • Next execution times are calculated based on your browser's local timezone and system clock.
  • Special characters L, W, and # are non-standard extensions supported by many cron implementations (e.g., Quartz, Spring, AWS).
  • Always test your cron expressions in the actual target environment before deploying.

References:
Tech Blog with curated related content
Web Tools Collection

Written by Hidekazu Konishi