Regular Expression Tester
Type a pattern and flags, paste some test text: matches are highlighted in real time, with captured groups and a live replace preview.
Type a pattern to get started.
Replace result:
Mini regex cheat sheet
| \d \w \s | digit, word character, whitespace (uppercase = negated) |
| . ^ $ | any character, start of line, end of line |
| * + ? {2,4} | 0+, 1+, 0 or 1, 2 to 4 repetitions |
| [abc] [^abc] | one of a, b, c — or none of them |
| (x) (?:x) (?<name>x) | capturing group, non-capturing, named |
| a|b \b | alternation, word boundary |
| (?=x) (?!x) | positive and negative lookahead |
The most useful flags in JavaScript regexes
The g (global) flag finds all matches instead of just the first one;
i makes the match case-insensitive; m makes ^ and
$ apply to each line rather than the whole text; s lets the dot
also match newlines; u enables proper Unicode handling (emoji, accented
characters, classes like \p{L}). Flags combine freely: gim is one
of the most common combinations. If you type an invalid or duplicate flag, this tester
flags it right away.
Capturing groups and replacements
Parentheses capture parts of the match that you can reuse in the replacement:
$1 is the first group, $2 the second, $& the
whole match. With named groups, such as (?<year>\d{4}), you can write
$<year>, which reads much better. A classic example: the pattern
(\d{2})/(\d{2})/(\d{4}) with the replacement $3-$1-$2 converts
dates from the US MM/DD/YYYY format to ISO format. Turn on replace mode above to see the
preview update live.