$ regex --test

regex tester.

Test regular expressions with real-time matching, group capture, and flags. 100% client-side.

input

pattern/\d{3}-\d{2}-\d{4}/gi

test string0 chars

matches

matches: 0

Enter a pattern and test string to see matches highlighted here.

What regex flavors are supported?

The tool uses JavaScript regex syntax (ECMAScript), supporting flags like g (global), i (case-insensitive), m (multiline), and s (dotall).

How do capture groups work?

Groups are defined with parentheses (). Each match's captured groups are shown below the test string. Named groups use (?<name>...) syntax.

What is the difference between test() and match()?

test() returns true/false if a match exists. match() returns the matched string and groups. The tool uses match() with detailed highlighting.

Essential Patterns

Pattern	Matches	Example
`.`	Any character	`a.c` → "abc", "a1c"
`\d`	Digit [0-9]	`\d+` → "123"
`\w`	Word char [a-zA-Z0-9_]	`\w+` → "hello_42"
`\s`	Whitespace	`a\sb` → "a b"
`^`	Start of string	`^Hello` → "Hello world"
`$`	End of string	`world$` → "Hello world"
`*`	0 or more	`ab*c` → "ac", "abc"
`+`	1 or more	`ab+c` → "abc", "abbc"
`?`	0 or 1 (optional)	`colou?r` → "color"
`{n,m}`	n to m times	`\d{3}` → "123"

Groups & Assertions

(abc)         — capture group
(?:abc)        — non-capturing group
(?<name>abc)   — named group
a(?=b)         — positive lookahead (a followed by b)
a(?!b)         — negative lookahead (a NOT followed by b)
(?<=a)b       — positive lookbehind (b preceded by a)
(?<!a)b       — negative lookbehind (b NOT preceded by a)

Performance tip: Avoid catastrophic backtracking by not nesting quantifiers like (a+)+. Use atomic groups or possessive quantifiers where supported, and always test with long strings.

learn more in our detailed guide.

→ read the guide