Developer toolLiveRuns on your device

Regex Tester

Write a JavaScript regular expression and see every match highlighted live, with capture groups, named groups and positions, plus a replace preview. Supports the g, i, m, s, u and y flags.

Pattern

Flags

Test text

Matches

Type a pattern to start.

Every match is highlighted here as you type.

Replace

Replacement

$1 or $<name> for groups, $& for the whole match, $$ for a literal $. Leave empty to delete every match.

The replaced text appears here.

⌘ ⇧ C copy

Matches

—

Groups

—

per match

Run time

—

In a background worker, stopped after 1 second.

Flags

g: Find every match, not just the first.
i: A and a match each other.
m: ^ and $ match at every line.
s: . matches line breaks too.
u: Whole code points, \p{…}, stricter syntax.
y: Each match must start where the last one ended.

Cheat sheet

.: Any character except a line break
\d \w \s: Digit, word character, whitespace
\D \W \S: Anything but those
[abc] [^abc]: One of a, b, c · anything else
[a-z]: A range of characters
^ $: Start · end (of each line with m)
\b: Word boundary
* + ?: 0 or more · 1 or more · optional
{3} {2,5}: Exactly 3 · between 2 and 5
*? +?: Lazy: as few as possible
(…): Capture group, $1 in replacements
(?<name>…): Named group, $<name>
(?:…): Group without capturing
a|b: a or b
(?=…) (?!…): Followed by · not followed by
(?<=…) (?<!…): Preceded by · not preceded by
\1 \k<name>: The same text a group matched
\p{L}: Any letter (needs u)

JavaScript (ECMAScript) syntax, exactly as this browser runs it.

How to use

Regex Tester in three steps

01
Type a pattern and choose flags.
02
Paste the text to test against.
03
Inspect matches and groups, or preview a replacement.

FAQ

Good to know

JavaScript (ECMAScript), exactly as your browser runs it — the same engine as Node.js and Chrome.

No. Patterns run in a background worker with a time limit, so a runaway pattern is stopped instead of locking up the tab.

No. The tool runs inside this browser tab. Your input is processed in memory on your device and is gone when you close the tab.

All Developer tools

Regex Tester

Matches

Replace

Regex Tester in three steps

Good to know

JSON Formatter

Base64 Encode / Decode

URL Encode / Decode

UUID Generator

Matches

Replace

Regex Tester in three steps

Good to know

01Which regex flavor is this?

02Can a bad pattern freeze the page?

03Is anything uploaded?

More developer tools

JSON Formatter

Base64 Encode / Decode

URL Encode / Decode

UUID Generator