The problem
Cron syntax is notoriously hard to verify — developers copy expressions from Stack Overflow or write their own, then paste them into random online parsers to check them, often without offline access or confidence in edge-case handling.
If you've hit this before, you know how it goes — you fire up a browser tab, paste the expression into crontab.guru, and hope it interprets edge cases the same way your cron daemon does.
As a solution, I created croncheck
Parse and preview cron expressions interactively — see the next 10 run times before you deploy
It's zero-dependency Node.js, so you can run it immediately without installing anything:
npx croncheck
Output:
croncheck "30 9 * * 1-5"
Expression: 30 9 * * 1-5
Meaning: minute 30, hour 9, every day, every month, weekdays 1-5
Next 10 run times:
1. Mon May 25 2026 09:30 in 4d 23h
2. Tue May 26 2026 09:30 in 5d 23h
3. Wed May 27 2026 09:30 in 6d 23h
4. Thu May 28 2026 09:30 in 7d 23h
5. Fri May 29 2026 09:30 in 8d 23h
6. Mon Jun 1 2026 09:30 in 11d 23h
7. Tue Jun 2 2026 09:30 in 12d 23h
8. Wed Jun 3 2026 09:30 in 13d 23h
9. Thu Jun 4 2026 09:30 in 14d 23h
10. Fri Jun 5 2026 09:30 in 15d 23h
How it works
Pure Node.js cron parser that expands each field (minute, hour, day, month, weekday) into a sorted array of valid values using set arithmetic, then advances a Date object forward one minute at a time to collect the next N matching timestamps, rendered in a raw-mode terminal UI.
Why I built it
Found repeated complaints on r/devops and HN from developers who deployed broken cron schedules after writing expressions from memory. Online tools like crontab.guru exist but require a browser and fail offline. No popular zero-dep npx tool fills the gap for quick in-terminal verification before committing a schedule to production.
Try it
npx croncheck --help
Part of µ micro — one new developer tool, shipped every day. All tools are zero-dependency Node.js and run instantly with npx.
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