Regex Tester
Test regular expressions with real-time match highlighting and capture group display. All processing happens in your browser.
Common Patterns Library
How to Test Regular Expressions
- 1
Enter Regex Pattern
Type your regular expression pattern in the pattern input field.
- 2
Set Flags
Toggle regex flags: g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode).
- 3
Enter Test String
Type or paste the text you want to test against in the test string area.
- 4
View Results
See real-time match highlighting, match count, indices, and captured groups.
About Regular Expressions
Regular expressions (regex or regexp) are powerful pattern-matching sequences used for searching, matching, extracting, and manipulating text. They are a fundamental tool in virtually every programming language (JavaScript, Python, Java, Go, Ruby, PHP), text editors (VS Code, Vim), command-line utilities (grep, sed, awk), and database systems. Mastering regex is an essential skill for developers and data engineers.
A regex pattern describes a set of strings using special syntax: . matches any character, * means zero or more, + means one or more, \d matches digits, \w matches word characters, and [...] defines character classes. Anchors like ^ (start) and $ (end) match positions, while quantifiers like {n,m} specify repetition counts. Parentheses () create capture groups for extracting specific parts of matches.
ToolPix's regex tester provides real-time feedback as you build your pattern — matches are instantly highlighted in the test string, capture groups are displayed with their indices, and the match count updates with every keystroke. A built-in common patterns library offers ready-made expressions for email, URL, phone, IP, and date validation.
All matching happens entirely in your browser using JavaScript's native RegExp engine — your patterns and test data are never sent to any server. Whether you are a beginner experimenting with basic patterns or an experienced developer debugging a complex lookahead, this free online regex tester gives you instant, private results.
Key Features
Common Use Cases
- •Test and debug regex patterns before using them in code
- •Validate email, URL, phone number, and date formats
- •Build search-and-replace patterns for text processing
- •Learn regex by experimenting with patterns and seeing results in real time
- •Extract specific data from log files or structured text
Frequently Asked Questions
What regex flavor does this tool use?
This tool uses JavaScript's built-in RegExp engine, which supports ECMAScript regex syntax. This is compatible with patterns used in Node.js, browsers, and most modern JavaScript environments.
What does the g (global) flag do?
Without the g flag, regex stops after the first match. With g enabled, it finds all matches in the test string. This is the most commonly used flag.
How do capture groups work?
Parentheses () in a regex create capture groups that extract specific parts of a match. For example, (\d{3})-(\d{4}) captures the two parts of a phone number separately.
Can I use lookbehind and lookahead?
Yes. JavaScript supports positive lookahead (?=...), negative lookahead (?!...), positive lookbehind (?<=...), and negative lookbehind (?<!...) in modern browsers.
Is my test data sent to a server?
No. All regex matching happens in your browser using JavaScript's native RegExp engine. Your patterns and test data remain completely private.
Is this regex tester free to use?
Yes. ToolPix's regex tester is completely free with no usage limits, no registration, and no restrictions on pattern complexity or test string length.
Can I use this on my phone?
Yes. The tester is fully responsive and works on all modern mobile browsers including iOS Safari and Chrome for Android.
Will my regex work the same in Python or Java?
Most basic patterns are cross-compatible. However, JavaScript regex has some differences — for example, it does not support possessive quantifiers (++), atomic groups, or certain Unicode property classes available in PCRE/Python. Always test in your target language for edge cases.
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