Regex Tester
Test and debug regular expressions with real-time pattern matching and visual highlighting
Introduction
Regular expressions (regex) are powerful pattern-matching tools used across programming languages for searching, validating, and manipulating text. Whether you're a seasoned developer debugging a complex pattern or a beginner trying to understand how regex syntax works, testing your patterns before deploying them into production code is essential. Our Regex Tester provides an interactive environment where you can experiment with regex patterns, see matches highlighted in real-time, and understand exactly what your pattern is capturing. The tool supports all JavaScript regex features including character classes, quantifiers, anchors, capture groups, lookaheads, lookbehinds, and Unicode handling. You can test patterns against any text—from simple email validation to complex log file parsing—and instantly see which parts of your text match, where they're located, and what gets captured in groups. The visual highlighting makes it immediately obvious whether your pattern is working as intended, and detailed error messages help you fix syntax problems quickly. With support for six different regex flags (global, case insensitive, multiline, dotAll, unicode, and sticky), you have complete control over how pattern matching behaves. Everything runs entirely in your browser with no server uploads, keeping your patterns and test data completely private. Sample patterns are included to help beginners learn regex syntax by example, making this tool perfect for both learning and professional development work.
Who Should Use This Tool?
- Web Developers building form validation for emails, phone numbers, usernames, and passwords
- Backend Engineers parsing log files to extract timestamps, IP addresses, and error messages
- Data Scientists cleaning text data and extracting structured information from unstructured text
- QA Engineers writing test cases to validate regex-based validation and parsing
- Security Professionals testing input sanitization patterns for SQL injection and XSS prevention
- DevOps Engineers building log monitoring and alerting systems
- Content Editors searching and replacing content patterns across documents
- Technical Writers documenting regex patterns with working examples
How This Tool Works
Enter your regex pattern using standard syntax including character classes (\\d, \\w, \\s), quantifiers (* + ? {n,m}), anchors (^ $), and capture groups. Select appropriate flags: g for global (find all matches), i for case insensitive, m for multiline mode, s for dotAll, u for unicode, and y for sticky matching. Input your test text in the text area, and the tool instantly highlights all matches with a yellow background in real-time as you type. Below the text, view detailed match information including match count, character positions, matched text, and captured groups if your pattern includes parentheses. If your pattern has syntax errors, clear error messages explain what needs fixing. Use sample patterns to learn common regex applications for emails, URLs, phone numbers, and more.
Try Regex Tester Now
Use the interactive tool below to get instant results
Real-Time Regex Testing
Test regular expressions instantly. All processing happens in your browser using JavaScript's RegExp engine.
Quick Samples
Regular Expression Pattern
Test String
🔤 Quick Reference
\d - Digit (0-9)\w - Word char\s - Whitespace. - Any char* - 0 or more+ - 1 or more? - 0 or 1^ - Start$ - End🚩 Flags Reference
- • g (global) - Find all matches instead of stopping after first
- • i (case insensitive) - Case-insensitive matching (A=a)
- • m (multiline) - ^ and $ match start/end of each line
- • s (dot all) - Dot (.) matches newline characters
- • u (unicode) - Enable full Unicode support
- • y (sticky) - Match only at lastIndex position
How to Use Regex Tester
Type Your Pattern
Enter your regex pattern using standard syntax: \d for digits, \w for letters/numbers, \s for spaces, * for zero or more, + for one or more, ? for optional. You can use anchors like ^ for start and $ for end. Parentheses create capture groups. If you are new to regex, hit the sample patterns button to see common examples.
Pick Your Flags
g (global) finds all matches instead of just the first one. i (case insensitive) ignores upper/lowercase differences. m (multiline) makes ^ and $ work per line instead of the whole string. s (dotAll) lets . match newlines. u (unicode) handles Unicode properly. y (sticky) is for exact position matching. You can combine multiple flags.
Paste Your Test Text
Put in the text you want to test your pattern against. Could be a single email address, a log file snippet, or a whole document. Matches get highlighted in yellow as you type so you can see what your pattern catches.
Check the Results
Matched text shows up highlighted. You will see how many matches were found, where they are in the text (position numbers), and any captured groups if you used parentheses. If your pattern has a syntax error, you will get an error message explaining what is wrong.
Use Cases for Regex Tester
Validating Form Inputs
Testing patterns for email addresses, phone numbers, zip codes, or credit card numbers before putting them in your form validation code. Make sure your pattern handles weird edge cases like international phone formats or email addresses with plus signs.
Parsing Log Files
Building patterns to pull timestamps, IP addresses, error codes, or status messages out of server logs. Test your pattern on sample log lines to make sure it catches what you need without grabbing extra junk.
Extracting Data
Pulling URLs, dates, prices, or product codes out of HTML, text files, or messy data. Test extraction on a few examples before running it on thousands of records so you know it works right.
Search and Replace
Designing patterns with capture groups for find-and-replace in your editor or code. Test the pattern first to make sure it replaces exactly what you want and does not break anything.
Learning Regex
Figuring out how regex syntax works by trying patterns and seeing what they match. Load sample patterns to see how \d, \w, +, *, and other symbols work. Way easier to learn by testing than just reading documentation.
Key Features
Instant Matching
Matches show up as you type with no delay
Yellow Highlights
Matched text gets highlighted in yellow so you can see what your pattern caught
Match Details
Shows how many matches, where they are (position numbers), and what got captured
Capture Groups
Displays captured groups separately if you used parentheses in your pattern
Six Flags
Global, case insensitive, multiline, dotAll, unicode, and sticky flags
Sample Patterns
Common regex examples you can load to see how patterns work
Error Messages
Tells you what is wrong if your pattern syntax is broken
Match Count
Tracks total matches and their positions in the text
Advanced Features
Lookaheads, lookbehinds, Unicode, and other complex regex stuff
No Uploads
Everything happens in your browser. Your patterns and test data stay private.
Frequently Asked Questions
What regex syntax is supported?
The tool uses JavaScript regex, which supports the standard stuff: \d for digits, \w for word characters (letters, numbers, underscore), \s for whitespace. Quantifiers like * (zero or more), + (one or more), ? (optional), {n,m} (specific counts). Anchors ^ (start) and $ (end). Parentheses for groups and capturing. Pipe | for alternation. Plus lookaheads, lookbehinds, and Unicode support. Basically everything you would use in JavaScript code.
How do the different flags work?
g (global) finds all matches instead of stopping after the first one—most people need this. i (case insensitive) treats A and a as the same. m (multiline) makes ^ and $ match the start/end of each line instead of the whole string. s (dotAll) lets . match newlines too. u (unicode) handles Unicode characters properly. y (sticky) is for advanced position-specific matching that most people do not need.
Why does my pattern only find one match?
You probably forgot to enable the g (global) flag. Without it, regex stops after finding the first match—that is just how regex works in every programming language. Check the g flag box and it will find all matches.
How do I use capture groups?
Put parentheses around the part you want to capture. For example, (\d+)-(\d+) captures the numbers on each side of a dash separately. If you test it on 123-456, group 1 is 123 and group 2 is 456. The tool shows captured groups under each match. If you need parentheses for grouping but do not want to capture, use (?:...) instead.
Is my test data private?
Yep. Everything runs in your browser. Your patterns and test text never leave your computer and do not get sent to any server. Safe to use with production data or sensitive patterns.