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About this tool
Date and time regex patterns for ISO 8601, DD/MM/YYYY, US dates, clock times and syslog or Apache log timestamps, with live testing.
The Regex Library for Dates provides seven copy-ready regular expressions for dates and times: ISO 8601 / RFC 3339 dates and timestamps, day-first DD/MM/YYYY and US MM/DD/YYYY slash dates, 24-hour and 12-hour clock times, the RFC 3164 syslog prefix and the Apache Common Log Format %t field. Digit ranges — months 01–12, days 01–31, hours 00–23, minutes and seconds 00–59 — are enforced by alternation, and every pattern documents exactly what a regex cannot check, like month lengths and leap years.
Open Regex Library for Dates on AltFTool — it loads instantly in your browser.
Choose one of the seven patterns from the 'Date / time format' dropdown — ISO 8601 date, ISO 8601 date-time (RFC 3339), DD/MM/YYYY, MM/DD/YYYY, clock time, syslog (RFC 3164) or Apache access log %t.
Type a value into 'Test a date, time or log line'; the verdict flips live between Match and No match, next to Accepts and Rejects example chips for the selected pattern.
Press Copy regex to copy the pattern as /source/flags, and read 'Known limitations of this pattern' for what regex cannot check — month lengths and leap years need a date parser.
Months cap at 12, days at 31 and hours at 23 through alternations, so 2026-13-01 and 24:00 fail instead of slipping through.
Syslog RFC 3164 and Apache CLF timestamp patterns are ready for grep, awk or extraction pipelines.
The DD/MM vs MM/DD overlap for days up to 12 is documented so you decide the convention per data source.
^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])$ matches YYYY-MM-DD with the month held to 01–12 and the day to 01–31. It cannot know that April has 30 days or apply leap-year rules — 2026-02-31 still passes — so parse the match with a date library to confirm the day exists.
Extend the date pattern with a T or space separator, hh:mm:ss where hours are ([01]\d|2[0-3]), optional fractional seconds, and an optional Z or ±hh:mm offset. The full pattern in this library accepts 2026-07-26T14:30:00Z and 2026-07-26 09:15:59.123+05:30 while rejecting minute or second values of 60.
Only when a value is out of range for one of them — 26/07/2026 can only be day-first because 26 exceeds 12 months, but 01/02/2026 matches both patterns and is genuinely ambiguous. The order must come from context (locale or data-source convention); no regex can recover it from the string alone.
Because per-month day counts and leap years are calendar logic, not string shape — encoding them in a regex needs a huge alternation per month plus a leap-year rule the regex cannot express cleanly. The standard practice is a two-step check: regex for format, then a date parser (like Date or a library) to verify the date really exists.