EventBridge cron/rate Expression Validator - AWS Schedule Tester with Next Run Times

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The EventBridge cron/rate Expression Validator is a purely client-side tool that parses Amazon EventBridge schedule expressions (6-field cron and rate), validates the AWS-specific rules, and previews when the rule will actually fire. All computation runs in your browser — no data is sent to any server, and no external libraries are loaded at runtime.

Client-side only. Your input never leaves the browser. This tool implements the AWS EventBridge cron dialect (6 fields including a Year field and ? wildcard). It is not the Unix/Linux 5-field cron dialect. Day-of-week is 1=SUN, 2=MON, ... 7=SAT, and exactly one of Day-of-month / Day-of-week must be ?.

  • This tool is provided "AS IS" without any warranties of any kind.
  • The author accepts no responsibility for missed, duplicated, or incorrectly timed schedule executions resulting from decisions made based on its output.
  • Always validate critical EventBridge schedules and rules in a non-production environment before deploying them.
  • 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.

Format: cron(minute hour day-of-month month day-of-week year) — 6 fields required. Or rate(value unit) where unit is minute[s] | hour[s] | day[s] (singular only when value is 1). Exactly one of day-of-month / day-of-week must be ?.

Summary

Field Breakdown

Next Runs (UTC / JST / Local)

Edit each field below. When you change Day-of-month or Day-of-week to a non-? value, the other field is automatically set to ? so the result stays AWS-valid.

FieldValueNotes
Minute 0-59, *, lists, ranges, */5
Hour 0-23 (UTC), *, lists, ranges, */N
Day-of-month 1-31, *, ?, L, LW, 15W
Month 1-12 or JAN-DEC, lists, ranges
Day-of-week 1-7 (1=SUN), or SUN-SAT, ?, 6L, 2#1
Year 1970-2199, *, lists, ranges, */N
Generated expression cron(0 12 * * ? *)

Features

  • Validates AWS EventBridge 6-field cron expressions and rate(value unit) expressions.
  • Enforces the ? exclusivity rule: exactly one of Day-of-month / Day-of-week must be ?.
  • Supports AWS-specific modifiers: L, LW, <n>W on Day-of-month and <dow>L, <dow>#<n> on Day-of-week.
  • Calculates the next 5 / 10 / 15 / 20 scheduled runs starting from Now (UTC) or a user-specified UTC time.
  • Displays each scheduled run in UTC, JST (UTC+9), and your browser's local timezone.
  • Provides a human-readable summary and a per-field breakdown of the parsed expression.
  • Includes a GUI builder that auto-synchronises ? between Day-of-month and Day-of-week.
  • Ships 16 real-world presets including every-5-minute, weekday-9-AM, last-Friday-6-PM, and rate examples.
  • Runs entirely in your browser — no servers, no external libraries, no analytics.

How to Use

  1. Enter an EventBridge expression such as cron(0 12 * * ? *) or rate(5 minutes), or pick a preset.
  2. Choose a base time: Now uses the current moment, Specific UTC lets you pick an exact UTC datetime.
  3. Select how many upcoming runs to display (5, 10, 15, or 20).
  4. Click Validate & Preview. Errors are shown in the message area; valid expressions produce a summary, field breakdown, and next-runs table.
  5. Use Copy Expression to copy the input, or Copy Schedule to copy the rendered next-runs table as plain text.
  6. Switch to Build cron to assemble an expression field-by-field. Changing Day-of-month or Day-of-week to a non-? value auto-sets the other to ?.
  7. Click Use in Validator in the Build tab to send the generated expression back to the Validate tab and preview it.

Important Notes

  • This tool implements the AWS EventBridge 6-field cron dialect, not Unix/Linux 5-field cron. The Year field is mandatory and the ? wildcard is AWS-specific.
  • Day-of-week numbering follows AWS: 1=SUN, 2=MON, 3=TUE, 4=WED, 5=THU, 6=FRI, 7=SAT. This differs from some other cron dialects.
  • All cron scheduling is evaluated in UTC, matching AWS EventBridge behaviour. JST and local-time columns are display conversions only.
  • The next-runs preview is a best-effort local calculation. AWS EventBridge may exhibit minor delivery delays and is not a real-time scheduler — actual invocation times can drift by seconds.
  • rate(...) expressions require the singular unit (minute, hour, day) only when the value is 1; otherwise use plural (minutes, hours, days).
  • Year range is limited to 1970-2199 per AWS documentation. Expressions that match no future date (for example cron(... 2020) in the future) will produce zero next runs.
  • No data is transmitted to any server. This page loads no third-party scripts and performs all parsing, validation, and scheduling locally in your browser.

References:
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Written by Hidekazu Konishi