Regex tester (JavaScript)

Enter a JavaScript regular expression and some text to highlight every match and inspect its capture groups as you type.

🔒 Runs entirely in your browser. Nothing you paste is uploaded or sent to a server.

Test string Matches

Replace with (optional: $1, $<name>, $&)

Result

Flags

Flag	Name	Effect
`g`	global	find all matches, not just the first
`i`	ignore case	`a` matches `A`
`m`	multiline	`^` and `$` match at every line break
`s`	dotAll	`.` also matches newlines
`u`	unicode	full Unicode, `\u{1F600}` and `\p{L}` escapes
`v`	unicodeSets	`u` plus set operations in classes (newer browsers)
`y`	sticky	match only at `lastIndex`
`d`	indices	record start/end of each group

Pattern	Matches
`.`	any character except newline
`\d` `\w` `\s`	digit, word character `[A-Za-z0-9_]`, whitespace
`\D` `\W` `\S`	the opposites
`[abc]` `[^abc]` `[a-z]`	one of, none of, range
`^` `$` `\b`	start, end, word boundary
`*` `+` `?` `{2,5}`	0+, 1+, optional, 2 to 5 times
`*?` `+?`	lazy (as few as possible)
`(…)` `(?:…)` `(?<name>…)`	capture, non-capturing, named group
`a\|b`	a or b
`(?=…)` `(?!…)` `(?<=…)` `(?<!…)`	lookahead, negative lookahead, lookbehind, negative lookbehind
`\1` `\k<name>`	backreference

In a string, backslashes must be doubled: new RegExp("\\d+") equals /\d+/. This tester takes the pattern as you would write it between slashes.
str.match(/x/g) returns only the matched strings, without groups; use str.matchAll(/x/g) to get groups for every match. matchAll and replaceAll throw a TypeError if the regex lacks the g flag.
A global regex keeps state in lastIndex, so calling re.test() repeatedly on different strings can alternate between true and false.
Calling .match() on something that is not a string fails with x.match is not a function; convert with String(x) first.
Patterns like (a+)+$ can backtrack catastrophically on long inputs and freeze the page (ReDoS). Prefer specific character classes over nested quantifiers.

Python's re, PCRE (PHP) and Go's RE2 differ in details: Python uses (?P<name>…), and RE2 has no lookarounds or backreferences.

Last updated 2026-11-01.