RegEx Tester

What is a RegEx Tester?

A regular expression (regex) is a pattern used to search, match, and manipulate text. Regex is incredibly powerful but notoriously hard to get right — a small change can completely alter what a pattern matches. A regex tester lets you experiment with a pattern against sample text and see exactly what it matches, instantly.

Our RegEx Tester uses the JavaScript regular-expression engine, the same one that runs in every browser and in Node.js. As you edit your pattern or test string, it highlights all matches, shows how many were found, and breaks out the contents of each capture group.

How to Use the RegEx Tester

• Type your pattern between the slashes at the top
• Toggle flags like global, ignore case, and multiline as needed
• Enter or paste the text you want to test against
• Matches are highlighted in the preview and counted automatically
• Each match is listed with its position and any capture-group values

Understanding Regex Flags

Flags modify how a pattern is applied. The global flag (g) finds all matches rather than stopping at the first. Ignore case (i) makes the match case-insensitive. Multiline (m) lets the anchors ^ and $ match at line breaks. Dotall (s) lets the dot match newline characters. Unicode (u) enables full Unicode matching, and sticky (y) anchors the match to the current position.

Combining the right flags is often the difference between a pattern that works and one that silently misses matches. This tester makes flags easy to toggle so you can see their effect immediately.

Common Uses for Regex

Developers use regular expressions to validate input like emails and phone numbers, search and replace across files, extract data from logs and text, parse structured strings, and define routing or tokenizing rules. A reliable tester is essential for building and debugging these patterns with confidence. All testing happens locally in your browser, so your patterns and data stay private.

Capture Groups and What They Do

Parentheses in a regular expression create capture groups, which do two jobs at once: they group part of the pattern so quantifiers and alternation apply to the whole group, and they remember the text that matched so you can extract it afterwards. When you match a date like 2024-01-15 with a pattern containing three parenthesized groups, you get not just the whole match but each piece — year, month, and day — as separate captured values ready to use.

This tester lists the capture groups for every match, which is invaluable when building patterns meant to extract structured data from text. You can see immediately whether each group is capturing what you expect, spot an off-by-one in your grouping, and confirm that optional groups behave correctly when the text they target is absent. Named groups and non-capturing groups behave as you would expect in the JavaScript engine the tool uses.

Why Choose Our RegEx Tester?

This tester is completely free, needs no signup, and runs entirely in your browser. It uses the real JavaScript regular-expression engine — the same one in every browser and in Node.js — so what you see here is exactly what your code will do. Matches are highlighted live, counted automatically, and broken out by capture group, and every flag is a simple toggle so you can watch its effect instantly.

The RegEx Tester is one of more than 200 free tools on ToopTools. If you write patterns regularly, you can pin it to your personalized My Workspace workspace so it sits beside your other developer utilities, always one click away. It works on any modern browser, on desktop and mobile.

Is the regex tester free?

Yes. It is completely free with no limits and no signup. You can test as many patterns against as much text as you like, as often as you like, without ever creating an account.

Which regex flavor does it use?

It uses the JavaScript (ECMAScript) regular-expression engine, the same one built into every web browser and Node.js. If you are writing regex for front-end or Node code, the results here match your runtime exactly. Note that some syntax differs from other flavors like PCRE, Python, or Java.

Does it show capture groups?

Yes. For each match, the tester lists the values captured by every parenthesized group, so you can confirm your pattern is extracting the right pieces of text. This is especially helpful when building patterns to pull structured data out of strings.

What do the flags do?

Each flag changes how the pattern is applied: global (g) finds all matches, ignore-case (i) matches regardless of case, multiline (m) makes the anchors match at line breaks, dotall (s) lets the dot match newlines, unicode (u) enables full Unicode matching, and sticky (y) anchors to the current position. You can toggle them and see the effect immediately.

Is my data private?

Completely. Both your pattern and your test text are processed locally in your browser, so nothing is uploaded, logged, or stored on a server. It is safe to test patterns against confidential data.

Tips for Writing Regular Expressions

• Build patterns incrementally, testing against sample text after each change
• Turn on the global flag when you expect more than one match
• Use capture groups to extract the specific pieces you need, not just to match
• Escape special characters like dots, plus signs, and parentheses when you mean them literally
• Prefer specific patterns over greedy catch-alls to avoid matching too much

Key Features

• Live match highlighting against your test text
• Toggles for all standard JavaScript regex flags
• Automatic match count and per-match capture-group details
• Uses the real JavaScript regex engine for accurate results
• Instant feedback as you edit the pattern or text
• 100% browser-based — your patterns and data never leave your device

How do I test a regular expression against text?

Type your regex pattern and paste your test text, and the tool highlights every match live as you type. It shows capture groups and lets you toggle flags, so you can refine the pattern until it matches exactly what you intend.

Does the regex tester work offline?

Yes. Matching runs entirely in your browser, so once the page has loaded the tool works without an internet connection and your pattern and test text are never uploaded — safe for testing against sensitive sample data.