What regex engine does this tester use?

The tester uses JavaScript's built-in RegExp engine, which runs entirely in your browser. This means the results exactly match what you'd get in any JavaScript application, including Node.js. If you're writing regex for Python, PHP, or another language, the syntax is largely the same for common patterns, but some advanced features like lookbehinds and named groups may behave differently — always verify against your target language's engine.

What regex flags are supported?

The tester supports all standard JavaScript regex flags: g (global — find all matches, not just the first), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — dot matches newlines too), and u (unicode). You can combine flags freely. Each flag takes effect immediately when toggled, so you can see the impact without re-running anything.

How do I test regex with capture groups?

Write your pattern with groups using parentheses — for example, (\d{4})-(\d{2})-(\d{2}) to capture year, month, and day from a date string. The tester will highlight the full match and list each capture group separately below the input, showing its matched value and position. Named groups using (? ...) syntax are also supported and displayed with their assigned names.

Is my test data safe? Does anything get sent to a server?

Nothing is sent anywhere. The regex tester runs entirely in your browser — your pattern and test string are processed locally using JavaScript's RegExp engine. No input is transmitted, stored, or logged. This makes it safe to test against real data, log samples, or any sensitive strings you're working with.

Can I use this to test regex for Python or PHP?

This tool uses the JavaScript regex engine, which shares most of its syntax with Python, PHP, and other PCRE-based engines. For common patterns — character classes, quantifiers, anchors, and basic groups — results will match across languages. For language-specific features like Python's verbose mode or PHP-specific flags, you may see differences. It is still highly useful for iterating on pattern logic before porting to your target language.

⚡ Speed Up Workflow⚡ Workflow

Regex Tester

Test and Debug Regular Expressions Online — Free Regex Tester

Pattern Engine

Flags:

//g

Test Payload

Match Coordinate Analysis

5 Matches Identified

Match 1Index: 0

Small

Group 1:Small

Match 2Index: 6

Tools

Group 1:Tools

Match 3Index: 19

Ultimate

Group 1:Ultimate

Match 4Index: 28

Developer

Group 1:Developer

Match 5Index: 38

Suite

Group 1:Suite

Test and Debug Patterns Live

Regex patterns are easy to get almost right and hard to get exactly right. A pattern that looks correct in your head produces zero matches in practice — or worse, matches more than you intended.

This Regex Tester gives you live match highlighting the moment you start typing. Write your pattern, set your flags, paste your test string — matches appear immediately, with capture groups and character positions shown below.

Quick Overview

Write your pattern live — matches update in real time as you type, no submit button needed.
Toggle flags instantly — switch g, i, m, s, and u flags on and off to see their effect immediately.
See every capture group — numbered and named groups are listed with matched values and positions.
Test against real strings safely — runs entirely in your browser; nothing is sent to any server.
Free, no account, no limit — test as many patterns and strings as you need without signing up.

Real-World Use Case

Marcus, a backend engineer, needed to extract tracking numbers from email subjects with inconsistent formats. He pasted 20 real subjects into the Utilx Regex Tester, toggled the gi flags, and iterated until his capture groups matched all 20 correctly — before touching his codebase.

Private & Secure

All match analysis happens locally in your browser context. We do not store, track, or cross-reference any patterns or test data, ensuring absolute privacy for your infrastructure secrets.

SECURE LOCAL COMPUTE

Live Highlighting

See matches update in real-time as you edit your pattern or test text.

Full Flag Support

Toggle g, i, m, s, and u flags individually to change pattern behaviour.

Capture Groups

Examine every numbered and named group with value and position details.

100% Client-Side

No server round-trips. Your data never leaves your browser sandbox.

Operational Workflow

ENTER PATTERN

Type your regular expression into the pattern field — no slashes needed.

SET FLAGS

Toggle flags like g, i, or m to control global search and case sensitivity.

PASTE TEST TEXT

Drop in the string you want to match against — matches highlight instantly.

READ DETAILS

Check match count and explore capture group output for every match.

When to Use This Tool

From validation patterns to log parsing, our regex tester is built for technical accuracy and speed.

Validation Logic

Test patterns for emails, phone numbers, or dates against sets of examples before coding.

Log Parsing

Iterate on extraction patterns against real log samples until capture groups are perfect.

Ecosystem Support

String Replace

Apply your validated regex as a find-and-replace operation.

URL Encoder

Encode special characters in a URL after extracting components.

JSON Formatter

Format and inspect JSON logs before parsing with regular expressions.

Privacy Statement

This tool runs 100% in your browser using JavaScript's native RegExp engine — your data is never sent to a server.

Browser Compatibility

Works in all modern browsers — Chrome, Firefox, Safari, and Edge — with no plugins required.

FAQs

The tester uses JavaScript's built-in RegExp engine, which runs directly in your browser. This means results exactly match what you would get in any JavaScript environment, including Node.js and browser-side code. For common patterns — character classes, quantifiers, anchors, and groups work the same way. Advanced features like atomic groups or possessive quantifiers are not supported in JavaScript's engine.

Data & Docs