⌘ K
12h · 24h · seconds · milliseconds · live

Build a custom time regex

Pick 12 or 24-hour, toggle seconds and milliseconds, require AM/PM. Verify samples live. Runs locally.

Time Regex Builder
Matches
1
samples
Failed
4
samples
Length
35
chars
Status
/
flag
options · build the regex
Separator
Test (one per line)
output · pattern + verification
Generated regex
/^(?:[01]\d|2[0-3]):[0-5]\d:[0-5]\d$/
Matches (1)
23:59:59
Non-matching (4)
23:59
12:00:00.123
11:30 AM
25:00
Quick Start

How to build a time regex

Switch 12/24-hour, toggle seconds and milliseconds, require AM/PM. Verify samples live.

  1. 01

    Pick clock

    24-hour for HH:MM. 12-hour with optional/required AM/PM.

    Patterns compile through the JavaScript RegExp constructor, so syntax errors surface immediately and engine quirks like Unicode property escapes (\p{L}) work when the u flag is on.

    patternECMAScriptliterallive
    input · literalclock · regex
    24h | 12h
    loaded · ECMAScriptPCRE · ready
  2. 02

    Add precision

    Toggle seconds and milliseconds based on your data shape.

    Each flag character mirrors the ECMAScript literal: g enables iteration, i folds case, m anchors per line, s lets . match newlines, u unlocks proper Unicode, y is sticky, and d emits indices.

    flagsoptionsg · i · mlive
    config · optionsprecision · flags
    HH:MM:SS.SSS
    flags applied · liveECMA · live
  3. 03

    Verify samples

    One time per line. 25:00 fails on 24h strict.

    Watch for catastrophic backtracking on nested quantifiers — a common ReDoS source. The tool caps match counts to keep the page responsive on pathological patterns.

    matchgroupshighlightReDoS-safe
    run · outputverify · matches
    ok 23:59 no 25:00
    matches · livegroups · live
  4. 04

    Copy or export

    Grab the output as JSON, CSV, or plain text — ready for your editor or pipeline.

    Copy writes via navigator.clipboard.writeText; downloads use a Blob and object URL, so nothing transits the network and the output is byte-identical to what you see on screen.

    copyexportclipboardblob
    export · exportedready · saved
    Copied
    ready to shipsuccess
Pro tips

Regex patterns that don't melt down

Use named groups

(?<year>\d{4}) reads better than $1 and survives reordering. Supported in ECMAScript 2018+.

Anchor strictly

Use ^/$ with the m flag when matching whole lines. Without anchors, partial matches sneak through.

Avoid catastrophic backtracking

Nested quantifiers like (a+)+ can explode. Run patterns through ReDoS Detector first.

Escape every literal

Backslash any meta character you want literally: \.\$\^\*\+\?\(\)\[\]\{\}\|\\.

Test edge cases

Empty string, single character, unicode, the maximum length you expect — write fixtures for each.

Patterns aren&rsquo;t parsers

Don’t parse HTML, JSON, or balanced parens with regex. Use a proper parser when the grammar is recursive.

Related toolsDate Regex BuilderRegex TesterRegex BuilderRegex LibraryRegex Character ClassesRegex Cheatsheet
Use Cases

When to build a time regex

Strict time validation per format and precision.

Log timestamps

Extract times from server logs. Compiles through the JavaScript RegExp constructor — engine quirks (Unicode property escapes, sticky matching, named groups) work when their flags are on. Error messages cite the exact position of any syntax issue.

ReDoS-safe

Form inputs

Validate appointment time fields. Pairs with the ReDoS detector to catch catastrophic backtracking before you deploy. A pattern that handles 1k-character input fine can become a denial-of-service vector on attacker-controlled 1M-character input.

ECMA-compliant

Schedule imports

Sanity-check time columns in CSV. Output exports as JavaScript, Python re, Java util.regex, .NET System.Text.RegularExpressions, PCRE, and POSIX — language quirks are highlighted on conversion so you don't ship a JS-only pattern to a Go service.

spec-grade

Sub-second precision

Validate millis for performance logs. Capture groups (named or numbered) round-trip cleanly into replacement strings, JSON output, or CSV extraction without re-typing. Backreferences ($1, ${name}) preserve semantics across languages.

cross-engine

12h-locale apps

Strict AM/PM for US-style fields. Test against edge cases — empty input, single character, max length, multibyte boundaries — to catch off-by-one and zero-length match bugs before they reach production.

test-ready

Teach time formats

Show how to range-restrict HH/MM/SS. All matching runs client-side so secret patterns never leave the browser. Useful when the pattern itself is sensitive (PII regexes, internal data formats, security filters).

production-ready
FAQ

Frequently asked questions

24-hour uses 00-23. 12-hour uses 1-12 (with optional leading zero).
Hours yes in 24h. Minutes and seconds always require leading zeros for < 10.
Not in this builder — handle Z and ±HH:MM separately or use the ISO 8601 datetime pattern.
Yes — 12-hour mode accepts both 1 and 01 for the hour.
No. The tool runs entirely in your browser — your pattern and sample text never leave the page.
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