A small web app that explains a five-field cron expression in plain English and lists its next 10 runs in your local time zone, for developers and operators who want to check a schedule before using it.
You have a crontab line or a CI schedule and want to be sure it fires when you think it does. Type the expression and read the description and the concrete upcoming run times, with validation errors shown inline. The cron parser is written in TypeScript with no cron library, and nothing is executed: cronsay only explains schedules.
Install Bun, clone this repository, then in the project directory run:
bun install
bun run dev
Open the local URL printed by Vite (by default http://localhost:5173/). The same commands work on Windows, macOS and Linux.
Type an expression in the input, or click a preset to fill it. A valid expression shows a description and the next 10 run times with a time zone name or offset. An invalid expression shows an inline error instead of stale results.
The field order is minute hour day-of-month month day-of-week:
| Expression | Schedule |
|---|---|
*/15 * * * * |
Every 15 minutes. |
0 9 * * 1-5 |
Monday through Friday at 09:00 local time. |
0 0 1 * * |
At midnight on the first day of each month. |
@daily |
Runs at 00:00, in local time. |
*/15 9-17 * * 1-5 |
"Runs every 15 minutes, during hours 09 through 17, on Monday through Friday, in local time." |
Under the list of runs, a line says how far apart the listed runs are: */15 * * * * shows Runs are 15 minutes apart. and 0 9 * * 1-5 shows:
Gaps between runs: shortest 1 day, longest 3 days.
The line is based on the runs that are listed, and gaps are elapsed time, so a daylight-saving change in your time zone can make a gap one hour longer or shorter (longest 31 days 1 hour). It is not shown when fewer than two runs are listed.
| Form | Meaning |
|---|---|
* |
Every value of the field |
5, 1,15,30 |
A value, or a list of values |
9-17 |
A range |
*/15, 10-30/5, 5/10 |
Positive steps; 5/10 runs from 5 through the field maximum in steps of 10 |
JAN-DEC, SUN-SAT |
Month and weekday names, case-insensitive |
0 or 7 |
Sunday |
@yearly, @annually, @monthly, @weekly, @daily, @midnight, @hourly |
Standard schedule macros |
The macros expand as follows: @yearly and @annually → 0 0 1 1 *; @monthly → 0 0 1 * *; @weekly → 0 0 * * 0; @daily and @midnight → 0 0 * * *; @hourly → 0 * * * *.
Six- and seven-field expressions, @reboot and other macros, and the special tokens ?, L, W and # are not supported. A six-field expression such as 0 0 9 * * * is rejected with a hint instead of the generic message: field count: got 6 fields, expected 5; a leading seconds field is not supported, so remove it (minute hour day-of-month month day-of-week). When both day-of-month and day-of-week are restricted, either may match (Vixie cron semantics).
Run times are strictly after the current time and use your browser's time zone. Nonexistent times in daylight-saving gaps are skipped. The search is bounded to about eight years, so a valid schedule that never matches, such as 0 0 31 2 *, shows a no-upcoming-runs message. Check the time zone and cron dialect of your real scheduler before relying on a schedule.
bun install
bun test
bun run typecheck
bun run lint
bun run build
Tests use bun:test for the parser, next-run calculator, descriptions, presets and UI interactions. bun run build writes the production site to dist/, and bun run preview serves that build locally. The package scripts contain no platform-specific shell syntax.
MIT, see LICENSE.
Built with BAKED, an open-source coding agent (bench loop round 02, BAKED ac45a9c).