Regex Tester & Matcher

About the Regex Tester & Matcher

Type a regular expression and some test text and see every match, its position and its capture groups update as you edit. Toggle the g, i, m, s and u flags, try a preset, and add a replacement pattern to preview the substituted text.

The tester uses JavaScript's regular expression engine, so results match what the pattern does in browsers and Node.js, not in PCRE, Python or Java.

How to use it

1. Type the pattern between the slashes and choose the flags you need.
2. Paste the text to test; every match, its position and its groups are listed as you type.
3. Optionally enter a replacement pattern such as $1-$2 to preview the substituted text, then press Copy Substituted (the button reads Copy Matches on the Matches tab).

Worked example

Capture groups are referenced as $1, $2, $3 in the replacement.

Pattern (\d{4})-(\d{2})-(\d{2}), flag g, text "Released 2026-10-13 and 2025-01-02", replacement $3/$2/$1

Matches: 2026-10-13 (groups 2026, 10, 13) and 2025-01-02 (groups 2025, 01, 02)
Replaced:  Released 13/10/2026 and 02/01/2025

Common mistakes and gotchas

• Without the g flag only the first match is reported.
• Syntax differs between languages. Possessive quantifiers, atomic groups and inline modifiers from PCRE do not exist in JavaScript, and a pattern copied from another language may be invalid here.
• Nested quantifiers such as (a+)+$ can backtrack catastrophically. The tester runs patterns with a time limit and refuses obviously dangerous ones instead of freezing the page.
• Inside a string literal in code, backslashes must be doubled ("\\d"); in this field you type the pattern itself, so write \d once.

Frequently asked questions