Developer builds cron expression explainer tool, shares key parsing lessons

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A developer who spent years copying cron expressions from Stack Overflow without truly understanding them decided to build a plain-English explainer tool from scratch. The tool parses any standard five-field cron expression, describes it in plain English, and displays the next five scheduled run times — all in roughly 50 lines of logic with no external libraries. Through the project, the developer documented core cron rules, including field order, supported operators like commas, hyphens, and slashes, and the acceptance of three-letter month and weekday names. One notable discovery was that day-of-month and day-of-week fields are OR'd rather than AND'd, meaning a job runs when either condition matches, not both simultaneously. The writeup aims to help other developers move beyond copy-pasting and actually read and reason through cron syntax themselves.

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