Cron Expression Parser & Next Run Calculator
About Cron Expression Parser
The cron expression parser validates a standard five-field Unix schedule, translates it into plain English, and calculates the dates and times when it will run next. Paste a crontab expression such as */15 9-17 * * 1-5 to check a deployment job, backup schedule, report, or recurring maintenance task before it reaches production.
Every calculation happens in your browser. The expression and generated run dates are not uploaded, stored, or evaluated on a remote service, making the tool useful for private infrastructure schedules. Choose browser-local time or UTC and preview five, ten, or twenty upcoming executions immediately.
This parser intentionally targets portable five-field Unix cron syntax: minute, hour, day of month, month, and day of week. It supports wildcards, comma-separated lists, ranges, steps, month names, and weekday names. Vendor-only extensions such as seconds, years, L, W, #, and Quartz question marks are rejected instead of being interpreted ambiguously.
How it works
Read the five cron fields
A Unix cron expression has five space-separated fields in this order: minute (0–59), hour (0–23), day of month (1–31), month (1–12), and day of week (0–7, where both 0 and 7 mean Sunday). The parser checks the field count and validates every value against its allowed range.
Use lists, ranges, and step values
An asterisk matches every value, a comma creates a list, a hyphen creates an inclusive range, and a slash applies a step. For example, */10 means every ten units, 9-17 limits the hours to the working day, and MON-FRI limits weekdays to Monday through Friday.
Understand day-of-month and weekday matching
Traditional Unix cron has an important rule: when both the day-of-month and day-of-week fields are restricted, a date runs when either field matches. When one field is an asterisk, the restricted field controls the date. The generated summary calls out this behavior for schedules where it matters.
Preview runs in local time or UTC
Select Local to evaluate calendar fields in the browser's time zone or UTC to remove local offset differences. Each result includes a readable date, an ISO 8601 timestamp, and Unix seconds. Daylight-saving transitions follow the selected browser time zone's calendar behavior.
Frequently asked questions
What cron syntax does this parser support?
It supports standard five-field Unix cron with numeric values, *, comma lists, inclusive ranges, positive steps, three-letter English month names, and three-letter English weekday names. It does not accept a seconds or year field.
Why does my Quartz or AWS cron expression fail?
Quartz, AWS EventBridge, and some schedulers use six or seven fields and add tokens such as ?, L, W, or #. Those are different dialects. This tool rejects them because translating vendor extensions as Unix cron could give you an unsafe schedule.
Are Sunday values 0 and 7 both accepted?
Yes. In the day-of-week field, both 0 and 7 are normalized to Sunday. You can also write SUN. Other weekdays use 1 through 6 or MON through SAT.
Which time zone is used for the next run calculation?
You choose browser-local time or UTC. Local mode uses the time zone configured on your device; UTC mode evaluates all five calendar fields in UTC. The chosen zone is stated in the result.
Is the cron expression sent to a server?
No. Parsing, validation, explanation, and next-run calculation all execute locally in the browser. Your schedules never leave the page.