Regex Tester & Builder

Test JavaScript regular expressions with live highlighting, capture groups, and find-and-replace preview.

Pattern

Test string0 chars

Highlighted matches0 matches

Match details

Replace

Result

Common regex presets

Cheat sheet

. — any char (except newline)

\\d \\D — digit / non-digit

\\w \\W — word char / non-word

\\s \\S — whitespace / non-whitespace

^ $ — start / end of string (or line with m)

\\b \\B — word boundary / non-boundary

* + ? {n,m} — repetition

[abc] [^abc] — character class / negated

(abc) — capture group

(?:abc) — non-capturing

(?<name>abc) — named group

a|b — alternation

(?=...) (?!...) — lookahead / neg.

(?<=...) (?<!...) — lookbehind / neg.

What this tool does

Test any JavaScript-flavoured regular expression against a block of text and see every match highlighted in real time. Each match shows its starting index, length, and the value of every capture group (including named groups). A built-in replace preview lets you verify find-and-replace operations before running them for real.

Regex flavours — are they all the same?

No. This tool uses the JavaScript (ECMAScript) regex engine, which is also the engine used inside modern browsers, Node.js, and most web tooling. It's very close to — but not identical to — PCRE (PHP, Perl), RE2 (Go), or Python's re. Key JS limitations to remember:

No atomic groups or possessive quantifiers.
No inline flag switching (?i).
Unicode property escapes (\p{Letter}) require the u flag.
Lookbehind (?<=...) is supported in modern browsers but was added later than lookahead.

Flag reference

g — global. Find all matches, not just the first.
i — case-insensitive.
m — multiline. ^ and $ match at line starts / ends.
s — "dotall". . also matches newlines.
u — Unicode. Treat the pattern as Unicode-aware; enables \p{}.
y — sticky. Match only from lastIndex.

Tips for common tasks

Parsing email addresses: the perfect email regex is notoriously hard. The preset here handles 99% of real emails — if you need full RFC 5322 compliance, use a library.
Replacing with capture groups: use $1, $2, etc. Named groups use $<name>.
Escape special characters in literal text: . * + ? ^ $ ( ) [ ] { } | \.
Test edge cases — empty strings, Unicode characters, whitespace-only input. The tool runs instantly, so iterate quickly.

ABOUT THIS TOOL

What is Regex Tester?

The Regex Tester by D&D Technology is a powerful online tool designed for developers to test JavaScript regular expressions seamlessly. With its intuitive interface, users can input their regex patterns and text, receiving immediate feedback through live highlighting. This feature allows for quick identification of matches and errors, making it an essential resource for both novice and experienced developers alike.

One of the standout features of the Regex Tester is its support for capture groups, enabling users to see how their regex patterns capture specific portions of the input text. This functionality is invaluable for debugging and refining regex patterns, ensuring that developers can achieve the desired results without hassle. Additionally, the tool includes 12 handy presets that cater to common regex scenarios, allowing users to start testing with pre-defined patterns and save time.

Ideal for web developers, software engineers, and anyone working with JavaScript, the Regex Tester simplifies the process of creating and validating regex expressions. Whether you're building a web application, validating user inputs, or searching through text data, this tool provides a reliable solution to streamline your workflow.

At D&D Technology, we understand the challenges developers face when working with complex patterns. That's why we designed the Regex Tester to be user-friendly and efficient, allowing you to focus on what matters most—building exceptional applications. Explore the capabilities of the Regex Tester today and enhance your development experience.

Ready to elevate your regex testing? Visit our Regex Tester tool now and start optimizing your JavaScript expressions with ease.

OUR PRODUCTS