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A browser-based github actions jst-to-utc cron generator tool. No data sent to server.

📘 How to Use

  1. Enter the desired execution time in Japan Standard Time (JST).
  2. Select the specific days of the week, or leave "Everyday" checked.

GitHub Actions JST-to-UTC Cron Generator

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GitHub Actions cron expressions can only be specified in UTC. Because of the calculation from JST, if the time crosses to the "previous day", the day of the week will also be shifted automatically.

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Article

GitHub Actions Cron JST to UTC Converter | Schedule Your Workflows in Japanese Time

This tool is for developers who need to schedule GitHub Actions cron jobs based on Japan Standard Time (JST). It instantly generates the correct UTC-based cron expression and YAML snippet, automatically handling the time and day-of-week conversion to prevent common scheduling errors.

💡 Tool Overview

  • Automatic JST to UTC Conversion: Instantly converts your desired JST schedule into the required UTC cron format for GitHub Actions.
  • Accurate Day-of-Week Correction: Automatically adjusts the day of the week when the UTC time falls on the previous day (e.g., jobs scheduled for early morning in JST).
  • Intuitive Day Selection: Easily select specific days for your job to run or use the "Everyday" toggle for daily tasks.
  • Ready-to-Use YAML Output: Generates a complete, copy-pasteable YAML snippet for the schedule trigger, including the original JST as a comment for easy reference.

🧐 Frequently Asked Questions

Q. Why can't I just specify JST directly in my GitHub Actions workflow?

A. GitHub's workflow scheduler operates exclusively on Coordinated Universal Time (UTC) to ensure consistency and avoid ambiguity across a global platform. This tool bridges the gap by correctly handling the -9 hour conversion from JST, including the tricky logic for date rollovers.

Q. I set a job for 5:00 AM JST on Monday, but the output cron runs on Sunday. Why?

A. This is the core problem this tool solves. 5:00 AM JST is 8:00 PM (20:00) UTC on the previous day (5 - 9 = -4; -4 + 24 = 20). The tool correctly calculates this time and day shift, ensuring your job runs precisely at the intended JST time.

📚 A Closer Look at GitHub Actions Cron Scheduling

The schedule event in GitHub Actions allows you to trigger a workflow at a specific UTC time using standard cron syntax. The format consists of five fields: minute hour day-of-month month day-of-week. While powerful, its reliance on UTC is a common source of confusion for developers working in other time zones.

Using UTC as a standard is crucial in distributed systems like GitHub to eliminate ambiguity related to regional time zones and Daylight Saving Time. By providing a single, universal time reference, UTC ensures that a scheduled task at "14:00" runs at the same absolute moment, regardless of where the developer or server is located. This tool simplifies adherence to that standard by offloading the mental math of time zone conversion.