Regular Expressions are powerful but notoriously difficult to master. Our Regex Tester provides a visual environment to build, test, and debug your patterns in real-time. Whether you are validating email formats or parsing complex logs, our tester gives you instant feedback and detailed explanations of your matches.
What is a Regex Tester?
A Regex Tester is a developer tool that allows you to input a regular expression pattern and a test string to see if they match. It visually highlights matches, captures groups, and provides an explanation of the regex logic, making it easier to identify errors and optimize patterns.
Why Use Our Regex Tester?
- Detect potential "ReDoS" (Regular Expression Denial of Service) issues
- Visual highlighting of matched groups and capturing brackets
- Instant validation as you type - no more trial and error in code
- Built-in cheat sheet with common tokens and syntax
- Support for multiple flags (Global, Case-Insensitive, Multi-line)
- Privacy-first: patterns are tested entirely in your browser
How to Test Your Regex
Enter Your Pattern
Input your regex (e.g., ^[a-z]+$) in the pattern field.
Provide Test String
Paste the text you want to test against in the input box.
Review Highlights
Check the real-time highlights to see what matched.
Refine & Adjust
Tweak your regex based on the visual feedback and captured groups.
Key Features
Real-time Matching
See results instantly as you type your regex or test string.
Match Highlights
Visually distinguishes between multiple matches and captured groups.
Detailed Explanations
Breaks down your regex token-by-token for easier understanding.
Pre-Defined Library
Access common regex snippets for emails, URLs, dates, and more.
Export to Code
Copy your finalized regex in formats for JavaScript, Python, or PHP.
Best Practices
- Use the least complex regex possible for better performance
- Always include the necessary flags (like /g) for your use case
- Test your patterns against "bad" input to ensure robust validation
- Comment complex regexes in your actual code for future maintenance
Common Use Cases
Form Validation
Testing patterns for email, password, and phone number inputs.
Data Extraction
Building patterns to scrape specific data from HTML or text docs.
Log Parsing
Creating expressions to extract structured data from server logs.
Content Moderation
Building filters for blacklisted words or patterns.
Frequently Asked Questions
Which engine is used?
We primarily use the JavaScript V8 engine; behavior may vary slightly for Python or PCRE.
Is it free?
Yes, completely free for all developers.
Does it support replacement?
Yes, you can also test regex replace operations.
Can it save my expressions?
Currently, it is session-based for your privacy.
Ready to Get Started?
100% browser-based. Your data never leaves your device.
Open Regular Expression (Regex) Tester