Regex Tester
Test regular expressions with live highlighting
Common Patterns
\d+ - Numbers\w+ - Words\s+ - Whitespace[a-z]+ - LowercaseFree Online Regex Tester - Test Regular Expressions Instantly
Welcome to DevToolVault's free online regex tester, the ultimate tool for testing and debugging regular expressions. Whether you're validating user input, parsing log files, or extracting data from text, our browser-based regex tool provides instant pattern matching with live highlighting—all without sending your data to any server.
What Are Regular Expressions and Why Use Them?
Regular expressions (regex or regexp) are powerful patterns used to match character combinations in strings. They're essential for developers working with text processing, form validation, data extraction, search and replace operations, log analysis, and web scraping. Understanding regex unlocks powerful text manipulation capabilities across virtually every programming language.
How to Use This Regex Tester
Our regex tester makes pattern testing simple and intuitive. Enter your regular expression pattern in the first field, specify flags (like g for global matching or i for case-insensitive), and paste your test string. The tool instantly highlights all matches and shows individual match results, helping you validate and refine your patterns in real-time.
Essential Regex Syntax Guide
- Character Classes: \d (digit), \w (word), \s (whitespace), [abc] (any of a,b,c), [^abc] (not a,b,c)
- Anchors: ^ (start), $ (end), \b (word boundary)
- Quantifiers: * (0+), + (1+), ? (0-1), {n} (exactly n), {n,m} (n to m times)
- Groups: (...) (capturing), (?:...) (non-capturing), (?<name>...) (named)
- Alternation: a|b (a or b), [...] (character set)
- Special: . (any char), \ (escape), (?=...) (lookahead), (?<=...) (lookbehind)
Common Regex Use Cases
Developers frequently use regex for email validation, phone number formatting, URL parsing, password strength checking, HTML tag extraction, IP address matching, date format validation, credit card number patterns, and extracting data from structured text. Our tester helps you build and verify these patterns before implementing them in your code.
Privacy-First Regex Testing
Unlike many online regex tools, DevToolVault processes everything locally in your browser using JavaScript's native RegExp engine. Your patterns, test strings, and sensitive data never leave your device. This makes our tool safe for testing patterns containing confidential information, API keys, passwords, or proprietary data formats.
Frequently Asked Questions
What is a regular expression (regex)?
A regular expression (regex) is a sequence of characters that defines a search pattern. It's used for pattern matching within strings, enabling powerful text search, validation, and manipulation operations in programming and text processing.
What do regex flags like g, i, and m mean?
Regex flags modify pattern behavior: g (global) finds all matches, i (case-insensitive) ignores letter case, m (multiline) treats each line as a separate string for ^ and $ anchors, s (dotAll) makes . match newlines, and u (unicode) enables full Unicode support.
How do I match email addresses with regex?
A basic email regex pattern is: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}. This matches most standard email formats, though complete RFC 5322 compliance requires a more complex pattern.
What is the difference between * and + quantifiers?
The * quantifier matches zero or more occurrences of the preceding element, while + matches one or more. For example, a* matches "", "a", "aa", etc., but a+ requires at least one "a", matching "a", "aa", etc.
How do capturing groups work in regex?
Capturing groups, created with parentheses (), save matched content for later reference. You can reference them with \1, \2, etc. Non-capturing groups (?:...) group patterns without saving, and named groups (?<name>...) allow descriptive references.
What are lookahead and lookbehind assertions?
Lookahead (?=...) and lookbehind (?<=...) are zero-width assertions that match positions based on what follows or precedes. Negative versions (?!...) and (?<!...) match when the pattern is NOT present. They don't consume characters.
Is my data secure when testing regex patterns?
Yes! Our regex tester processes everything in your browser using JavaScript's native RegExp engine. No data is sent to servers. Your patterns and test strings remain completely private on your device.
How can I optimize regex performance?
Optimize regex by: being specific (avoid .* when possible), using non-capturing groups, anchoring patterns with ^ and $, avoiding nested quantifiers, using character classes instead of alternation, and testing with realistic data sizes.
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