Syntax & Fields
A cron expression is just five fields separated by spaces, each one answering a different question about "when." Once you can read the five slots in order, you can read almost any cron expression you'll ever encounter.
💡 The Bottom Line
A cron expression always has five fields, in this fixed order: minute, hour, day of month,
month, and day of week. Each field either names a specific value or uses * to mean
"every value is fine here."
The five fields, in order
* * * * *
| | | | |
| | | | +----- day of week (0-6, Sunday = 0)
| | | +----------- month (1-12)
| | +----------------- day of month (1-31)
| +----------------------- hour (0-23)
+----------------------------- minute (0-59)Read left to right, that's: minute, hour, day-of-month, month, day-of-week. Every cron expression, no matter how complex it looks, is built from exactly these five slots — nothing more.
📋 The five fields, with their allowed values
- Minute —
0–59 - Hour —
0–23(24-hour clock, no AM/PM) - Day of month —
1–31 - Month —
1–12(1= January) - Day of week —
0–6(0= Sunday — see Lesson 6 for a gotcha here)
A first concrete example
0 9 * * *Reading it field by field: minute 0, hour 9, then *,
*, * for day-of-month, month, and day-of-week — meaning "don't
restrict those, any value is fine." Put together: at minute 0 of hour 9, every day of
every month, on every day of the week — in plain English, every day at
9:00am.
⚠️ Watch Out
The hour field is 24-hour time, not 12-hour AM/PM. 9 means
9am, but 5pm is 17, not 5. Writing 0 5 * * * when you
meant 5pm is one of the most common first-time cron mistakes — it actually schedules the job
for 5am.
🙋 There Are No Dumb Questions
Q: What happens if I leave a field blank instead of using *?
A: You can't — a standard cron expression always needs all five fields present and
space-separated. Leaving one out isn't "default to every value," it's a malformed expression
that most parsers will reject outright. Use * explicitly whenever you mean "any
value is fine here."
🔧 Try It Yourself
Before reading further in this track, try to write the cron expression for "every day at
6:30pm" using just what you've learned so far: minute, hour (remember 24-hour time), then three
asterisks. Check your answer: it should be 30 18 * * *.
✅ Quick Check
In the expression 0 9 * * *, what does the second field (9)
represent?
Next up: a set of common, ready-to-use schedules that will cover most of the recurring jobs you'll ever need to write.