A powerful, visual, and real-time Regular Expression testing environment. Build, debug, and share complex patterns with advanced highlighting.
Enter a pattern and test string to see matches
Regular Expressions (Regex) are an indispensable tool in every developer's arsenal. Whether you are validating email addresses on a frontend form, parsing gigabytes of server logs, or performing complex text replacements in your IDE, regex allows you to define flexible search patterns. Our Professional Online Regex Tester provides an immersive, 100% client-side environment to build, validate, debug, and share complex regular expressions securely in real-time.
Building a regular expression from scratch can be a daunting process. The syntax is notoriously cryptic, and a single misplaced character can lead to catastrophic backtracking or missed matches. Our tool mitigates these issues by providing instant visual feedback.
Unlike server-side regex testers, all matching and parsing occurs directly in your browser. This means you can safely test regex patterns against sensitive customer data, API keys, or proprietary logs without fear of data leakage. Your text strings never leave your local machine.
Understanding capture groups is one of the hardest parts of regex. Our engine automatically color-codes capture groups within your match results, making it trivial to see exactly which part of your pattern matched which substring.
Save your most frequently used patterns directly to your browser's local storage. Need to share a complex pattern with a coworker? Generate a shareable URL that preserves your pattern, flags, and test string instantly.
As you type your pattern, our visual explanation engine breaks it down. Hover over the colorful tokens to understand exactly what `\b`, `(?=...)`, or `[^a-z]` actually means in the context of your specific regular expression.
If you are new to regular expressions, here is a quick reference guide to the most common tokens you will use when building your patterns.
| Token | Description | Example |
|---|---|---|
| \d | Matches any single digit (equivalent to [0-9]). | `\d\d` matches "42" |
| \w | Matches any word character (alphanumeric and underscore). | `\w+` matches "username_1" |
| ^ and $ | Anchors. Matches the beginning (^) or end ($) of the string or line. | `^Start` matches only at the beginning |
| * and + | Quantifiers. * means 0 or more times. + means 1 or more times. | `a+` matches "a", "aa", "aaa" |
| [a-z] | Character class. Matches any character in the specified range. | `[A-Z]` matches "B" but not "b" |
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$
While RFC 5322 dictates a much more complex standard for email validation, this practical regex catches 99% of valid email addresses without being overly permissive. It ensures there is an alphanumeric local part, an @ symbol, a domain name, and a TLD of at least two characters.
^(?=.*[A-Za-z])(?=.*\d)(?=.*[@$!%*#?&])[A-Za-z\d@$!%*#?&]{8,}$
This pattern uses positive lookaheads `(?=...)` to enforce password complexity. It requires a minimum of 8 characters, at least one letter, at least one number, and at least one special character, ensuring robust security for user authentication systems.
https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)
A robust pattern for scraping or hyperlinking. It optionally matches HTTP or HTTPS, the www subdomain, followed by the domain name and any valid URL path or query string parameters.
Our regex tester uses the JavaScript (ECMAScript) regex engine built directly into your web browser. This means patterns tested here will behave exactly identically in Node.js, React, and Vanilla JS environments. However, the syntax is highly compatible with PCRE (PHP, Perl), Python, and Java regex flavors for 95% of common use cases.
Flags modify how the search is performed. g (Global) finds all matches rather than stopping after the first. i (Ignore Case) makes `a` match `A`. m (Multiline) changes the behavior of `^` and `$` to match the start/end of lines, not just the whole string. s (DotAll) allows the dot `.` to match newline characters.
Because processing occurs in your browser's memory, there is no hard limit imposed by our servers. You can easily paste megabytes of log files. However, extremely poorly written regex patterns can suffer from "Catastrophic Backtracking" which might temporarily freeze your browser tab on massive text blocks.
When you wrap a part of your regex in parentheses like `(\w+)`, it creates a capture group. Our tool highlights these groups with specific colors in the results pane. If you hover over the highlighted match, it will display a tooltip identifying which capture group (e.g., Group 1, Group 2) matched that specific text.
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