quartz-cron-checker

quartz-cron-checker is a lightweight (zero dependencies!), strict validator for Quartz-style cron expressions in Python.

It ensures all parts of the cron string conform to the Quartz cron spec—including support for special characters, named values, and mutual exclusivity of day-of-month and day-of-week.

Features

• ✅ Full support for 6- or 7-field Quartz cron expressions (second minute hour day-of-month month day-of-week [year])
• ✅ Literal handling (*, ?, L, W, #)
• ✅ Named months (JAN, FEB, etc.) and days (MON, TUE, etc.)
• ✅ Detailed error messages and exceptions
• ✅ Clean object-oriented API
• ✅ Extensible field-level validation

Installation

pip install quartz-cron-checker

Usage

Calling validate will raise an exception if the cron string is invalid. The method will return True otherwise.

from quartz_cron_checker import QuartzCronChecker

# Parse and validate a cron string
cron = QuartzCronChecker.from_cron_string("0 0 12 ? * MON-FRI")
cron.validate()  # Raises if invalid

# __str__ returns the original cron string
print(cron)
>>> 0 0 12 ? * MON-FRI

# __repr__ returns a more detailed representation
print(repr(cron))
>>> <QuartzCronChecker(second=0, minute=0, hour=12, day_of_month=?, month=*, day_of_week=MON-FRI, year=None)>

You can also validate either a whole cron string or individual fields without creating an object:

from quartz_cron_checker import validate_cron_string, validate_day_of_month, validate_second

# Validate a full cron string
print(validate_cron_string("0 0 12 ? * MON-FRI"))
>>> True

print(validate_cron_string("0 0 12 ? * MON-FRI-SAT"))
>>> PatternOrLiteralMatchError: [day_of_week=MON-FRI-SAT] Part 'MON-FRI-SAT' does not match any literal (THU, FRI, MON, SAT, TUE, WED, *, SUN, ?) or allowed pattern (Range, Increment, Range with increment, List of digits, Day of week occurrence, Last day of week in month, Day of week range, Specific day of week)


# Validate individual fields
print(validate_second("0"))
>>> True

print(validate_day_of_month("13/26"))
>>> True

print(validate_day_of_month("31W"))
>>> True

print(validate_day_of_month("33W"))
>>> PatternValidatorError: [day_of_month=33W] Part '33W' matches pattern 'Nearest weekday' ('^(\d+)W$') but failed semantic validation: must be between 1 and 31