Regex Tester

Test regex

Enter a pattern and sample text. See matches, groups, and replacements update as you type.

Runs in your browser. Inputs stay on this device — nothing is uploaded to BrowserSpaces for processing.

Flags

g, i, m, s, u, y.

Groups

Numbered and named captures.

Replace

Preview substitutions.

Errors

Invalid patterns explained.

Use the tool

Pathological patterns can freeze this tab (ReDoS). Keep samples modest; matches are capped at 500.

PatternFlags

Replace template

Sample text

9 match(es)

@0 The
@4 quick
@10 brown
@16 fox
@20 jumps
@26 over
@31 the
@35 lazy
@40 dog

Replace preview

The quick brown fox jumps over the lazy dog.

How it works

Native RegExp

Patterns compile as JavaScript RegExp objects in your tab — same engine your app would use. Pathological patterns can freeze the tab (ReDoS); keep samples modest.

Before you start

Avoid nested quantifiers on large inputs — they can hang the browser.

Three steps

1
Write a pattern
Plus flags.
2
Paste sample text
Matches appear live.
3
Replace
Optional substitution preview.