Regex tool

Test a JavaScript regular expression against sample text with live highlighting, and keep the syntax cheatsheet at hand. Everything happens locally in your browser.

Cheatsheet

Common JavaScript regular expression syntax at a glance.

Character classes

.: Any character except newline (with s, anything). a.c matches "abc", "axc".
\d \D: Digit / non-digit. \d\d matches "42".
\w \W: Word character [A-Za-z0-9_] / non-word character.
\s \S: Whitespace / non-whitespace. \S+ matches each word.
[abc] [^abc]: One of the listed characters / any character not listed. [a-z0-9] is a range.
\p{L}: Unicode property escape (needs the u flag): any letter, including "é" and "日".
\.: A backslash makes a special character literal: a\.c matches "a.c" only.

Quantifiers

*: Zero or more. ab*c matches "ac" and "abbc".
+: One or more. ab+c needs at least one "b".
?: Zero or one. colou?r matches "color" and "colour".
{3} {2,5} {2,}: Exactly 3 / between 2 and 5 / at least 2 repetitions. \d{3} matches "123".
*? +? {2,5}?: Lazy versions: match as little as possible. <.+?> matches "<a>" in "<a><b>".

Anchors & boundaries

^: Start of string (start of line with m). ^abc rejects "xabc".
$: End of string (end of line with m). \d+$ matches the trailing "123".
\b: Word boundary. \bcat\b matches "a cat", not "concat".
\B: Non-word boundary: the opposite of \b.

Groups & backreferences

(abc): Capturing group. (ab)+ matches "abab" and remembers it as $1.
(?:abc): Non-capturing group: group without remembering.
(?<name>abc): Named group. (?<year>\d{4}) stores the year under year.
\1 \k<name>: Backreference to group 1 / to a named group. (\w+) \1 matches "hey hey".
a|b: Alternation. cat|dog matches either word.

Lookarounds

(?=abc): Positive lookahead. \d+(?=px) matches the 12 in "12px" but not in "12em".
(?!abc): Negative lookahead: only when abc does not follow.
(?<=abc): Positive lookbehind. (?<=\$)\d+ matches the 5 in "$5".
(?<!abc): Negative lookbehind: only when abc does not precede.

Flags

g: Global: find all matches, not just the first.
i: Ignore case: /abc/i matches "ABC".
m: Multiline: ^ and $ match every line.
s: DotAll: . also matches newlines.
u: Unicode: full code-point matching, enables \p{…}.