Cron Expression Parser
Parse cron expressions
Format: minute hour day-of-month month day-of-week
What Is This Tool?
The Cron Expression Parser explains a standard 5-field cron expression in plain English and shows the next 5 times it would run, computed by simulating forward from the current time. Everything runs locally in your browser using a hand-written rule-based analyzer — no server involved.
How to Use
Type a 5-field cron expression, or click one of the example buttons.
The description updates automatically to explain what it means.
Check the next 5 run times computed from right now.
Invalid fields are flagged with a clear error message.
Features
- Plain-English explanation of minute, hour, day, month, and weekday fields
- Supports *, single values, comma lists, ranges, and step values
- Computes the next 5 matching run times from the current time
- Validates field count and out-of-range values
- Five common example expressions, one click away
- 100% client-side — nothing leaves your browser
Examples
Expression: 0 9 * * 1-5
Description: At minute 0 past hour 9 on every day-of-month, on every month, on every day-of-week from Monday through Friday.
Common Use Cases
- Understanding an unfamiliar cron schedule found in a codebase
- Double-checking a schedule before deploying a scheduled job
- Learning cron syntax through common example expressions
- Verifying when a job will next actually run
Frequently Asked Questions
Is my cron expression uploaded anywhere?
No. Parsing and simulation happen entirely in your browser using JavaScript. Nothing is sent to a server.
Does this support seconds or shorthand like @daily?
No. Only the standard 5-field cron format (minute hour day-of-month month day-of-week) is supported. Seconds fields and shorthand expressions such as @yearly or @reboot are not handled.
What values are valid for each field?
Minute: 0-59. Hour: 0-23. Day-of-month: 1-31. Month: 1-12. Day-of-week: 0-6 (0 is Sunday). Each field also accepts *, comma lists, ranges (a-b), and step values (*/n).
How are the next run times calculated?
The tool simulates forward minute by minute from the current time, checking each candidate time against all five fields, until it finds 5 matches or gives up after searching about 4 years.
What happens with an invalid expression?
The tool validates the field count and the numeric ranges before analyzing, and shows a clear error message if something doesn't match the standard 5-field format.
Does day-of-month AND day-of-week both apply together?
Yes, this tool requires both the day-of-month and day-of-week fields to match (a simple AND), unlike some cron implementations that use OR when both are restricted.