I finally understood cron expressions by building an explainer for them

For years I copied cron expressions off Stack Overflow, pasted them into a config file, crossed my fingers, and moved on. 0 9 * * 1-5? Sure, that "looks like weekday morning." */15 * * * *? "Every 15 minutes, probably." I never actually read them. So I did the thing that always cures this for me: I built a tool that parses a cron expression, explains it in plain English, and shows the next five times it will fire. No library. About 50 lines of real logic. Here's everything I learned. A standard