What regex flavor does this support?

This tool uses the JavaScript RegExp engine built into your browser. It supports most standard regex syntax including character classes, quantifiers, lookaheads, lookbehinds (ES2018+), named capture groups, and Unicode property escapes with the u flag.

How do I match a literal dot?

Escape it with a backslash: \. A bare dot (.) matches any character except a newline. Use \. when you want exactly a period, for example in an email or IP address pattern.

What does the 'g' flag do?

The global (g) flag tells the engine to find all non-overlapping matches in the string rather than stopping after the first one. Without g, only the first match is returned and highlighted.

Why is my regex slow or causing catastrophic backtracking?

Catastrophic backtracking happens when nested quantifiers (like (a+)+ or (.*).*) can match the same characters in exponentially many ways. To avoid it: be specific with character classes, use atomic groups or possessive quantifiers where your engine supports them, and test against long strings with no match to expose worst-case behavior.

Regex Tester

Name: Regex Tester
Availability: InStock
Author: Nham Vu

Type a regex pattern and test string to instantly see highlighted matches, capture groups, and a replacement preview — all in your browser using JavaScript RegExp.

Pattern

/ g

Flags:

Test String

Match Preview 0 matches

Matches will be highlighted here...

Match Details

No matches yet.

. Any character except newline

\d Digit (0–9)

\D Non-digit

\w Word character (a-z, A-Z, 0-9, _)

\W Non-word character

\s Whitespace (space, tab, newline…)

\S Non-whitespace

^ Start of string (or line with m)

$ End of string (or line with m)

\b Word boundary

\B Non-word boundary

* Zero or more (greedy)

+ One or more (greedy)

? Zero or one (or lazy modifier)

{n} Exactly n repetitions

{n,m} Between n and m repetitions

(abc) Capture group

(?:abc) Non-capturing group

(?<name>abc) Named capture group

(?=abc) Positive lookahead

(?!abc) Negative lookahead

(?<=abc) Positive lookbehind

(?<!abc) Negative lookbehind

[abc] Character class — a, b, or c

[^abc] Negated class — not a, b, or c

[a-z] Character range a through z

a|b Alternation — a or b

\\ Literal backslash

\. Literal dot

Summary

Type a regex pattern and test string to instantly see highlighted matches, capture groups, and a replacement preview — all in your browser using JavaScript RegExp.

How it works

Enter a regex pattern in the Pattern field (without surrounding slashes).
Toggle any flags you need — g (global), i (case-insensitive), m (multiline), s (dot-all), u (unicode), y (sticky).
Paste or type the text you want to test in the Test String area.
Matches are highlighted in yellow in real time. Expand the Replace section to preview substitutions using $1, $&, or named groups.

Use cases

Validating form input such as emails, phone numbers, and postal codes
Extracting structured data like IP addresses or timestamps from log files
Search-and-replace operations in code editors and data pipelines

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu