Developer Tools

Regex Tester & Pattern Library

Live regex testing plus a curated library of patterns engineers actually need every day — IPv4, CIDR, AWS ARN, JWT, UUID, semver, Kubernetes, Docker and more. Click a pattern to load it.

Free Tool100% Local25 patterns

Privacy: regex execution and matching happen client-side. Your pattern and test text never leave the browser.

Pattern

3 matches

//g

Test text

Highlighted matches

192.168.1.1
10.0.0.0
255.255.255.255
299.1.1.1 ← invalid
localhost

Match details

#	Match	Index	Groups
1	192.168.1.1	0	$1: 1.$2: 1$3: 1
2	10.0.0.0	12	$1: 0.$2: 0$3: 0
3	255.255.255.255	21	$1: 255.$2: 255$3: 255

Pattern library

How the library is curated

These patterns are the ones I actually paste into PRs and pipelines. They favour the common case over RFC purity — a 600-character RFC 5322 email regex matches addresses no production system uses. If you need stricter validation, use a dedicated parser instead of a regex.

Flag cheatsheet

g — find all matches; without it, only the first match is returned.
i — case-insensitive.
m — ^ and $ match at line boundaries (use with multiline input).
s — . matches newlines too.
u — full unicode mode; required for unicode property escapes like \p{L}.
y — sticky: matches must start at lastIndex. Rarely useful outside of tokenisers.

Gotchas

Catastrophic backtracking. Nested quantifiers like (a+)+ on long input can hang the engine for seconds.
ECMAScript flavor. No atomic groups, no possessive quantifiers, no lookbehind in older Safari — this tester uses your browser's engine, so what works here works in Node.
Anchors and multiline. ^ and $ default to start/end of the whole string. Add m to make them per-line.

Frequently Asked Questions

Which regex flavor does this tester use?

ECMAScript RegExp — the browser's native engine. Same syntax as Node.js and Deno. May differ from PCRE / Python / Go regex flavors.

Are the library patterns RFC-strict?

Most are practical, not strict. They aim for the common case. For full validation use a dedicated parser.

Does this tool send my pattern or test text anywhere?

No. Everything runs in your browser. Open DevTools → Network — no requests fire.

Why is my pattern slow or hanging?

Catastrophic backtracking. Nested quantifiers like (a+)+ on long input explode exponentially. Refactor with explicit alternation or anchors.