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Online Regex Tester & Debugger

Master regular expressions with our comprehensive online regex tester. Instantly test, debug, and validate your regex patterns with real-time matching, detailed capture group analysis, and support for all common flags. Perfect for developers, data analysts, and anyone working with text processing. Features include a complete regex cheat sheet, common pattern library, and export capabilities.

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Initializing JSON Engine...

Preparing local environment

How to Use Regex Tester

1

Input Your Pattern

Enter your regular expression in the pattern field. Don't include the surrounding slashes - just the pattern itself.

2

Add Test Text

Paste or type the text you want to test your regex against in the test text area below the pattern input.

3

Analyze Results

View highlighted matches and detailed breakdown of capture groups in the results section below.

Pro Tips for Regex Testing

Validation Use Cases

  • • Validate email formats with our pre-built pattern
  • • Check phone numbers for correct formatting
  • • Verify URL structures and protocols
  • • Ensure password complexity requirements

Data Extraction

  • • Use parentheses to create capture groups
  • • Extract specific fields from structured text
  • • Parse log files for error messages
  • • Pull data from API responses

Efficiency Tips

  • • Start simple and build complexity gradually
  • • Use non-greedy quantifiers when appropriate
  • • Test with various edge cases
  • • Enable flags for case-insensitive matching

Debugging Techniques

  • • Check for unmatched parentheses
  • • Verify escape sequences are correct
  • • Test with small samples first
  • • Use our sample text for quick experimentation

Powerful Regex Testing Features

Real-Time Matching

See all matches highlighted instantly as you type your pattern or modify your test text.

Capture Group Analysis

Detailed breakdown of all captured groups for each match to help with data extraction.

Flag Support

Toggle common flags like global, case-insensitive, multiline, and more to test different scenarios.

Common Patterns Library

Access a collection of pre-built patterns for common use cases like emails, URLs, and phone numbers.

Privacy Focused

All processing happens in your browser - your patterns and text never leave your computer.

Export Capabilities

Save your test results and matches as JSON files for documentation or further analysis.

Master Regular Expressions: A Guide & Cheat Sheet

Why Use an Online Regex Tester?

Writing regular expressions can be a complex and error-prone process. A "blind" approach often leads to frustration and bugs. Our online regex tester provides an interactive environment to build and debug patterns with confidence, offering several key advantages:

  • Instant Feedback: See matches appear and disappear in real-time as you type your pattern.
  • Visual Highlighting: Quickly identify all matching parts of your test string.
  • Capture Group Analysis: Easily inspect the data captured by each group to ensure your logic is correct.
  • Flag Emulation: Toggle flags like global (`g`), case-insensitive (`i`), and multiline (`m`) to understand their impact instantly.
  • Risk-Free Learning: Experiment with complex patterns and syntax without affecting any production code.

Regex Cheat Sheet: Core Concepts

Use this quick reference to build and understand common regex components. Test them in the editor above!

Character Classes

. - Any character except newline
\d - Any digit (0-9)
\D - Any non-digit
\w - Word character (a-z, A-Z, 0-9, _)
\W - Any non-word character
\s - Whitespace character
[abc] - Matches a, b, or c
[^abc] - Matches any character except a, b, or c

Quantifiers

* - 0 or more times
+ - 1 or more times
? - 0 or 1 time (makes it optional)
{n} - Exactly n times
{n,} - n or more times
{n,m} - Between n and m times
*? - Non-greedy version of *

Anchors & Groups

^ - Start of the string
$ - End of the string
\b - Word boundary
\B - Non-word boundary
() - Capture group
(?:...) - Non-capturing group
| - Alternation (OR operator)

Practical Use Cases

  • Form Validation: Ensure user input matches required formats for emails, phone numbers, passwords, and postal codes.
  • Log File Analysis: Extract specific information like IP addresses, timestamps, or error codes from large log files.
  • Web Scraping: Find and extract specific data points, like product prices or article titles, from HTML content.
  • Code Refactoring: Perform powerful search-and-replace operations across multiple files in code editors like VS Code.
Frequently Asked Questions
What is a regular expression (regex)?

A regular expression is a sequence of characters that specifies a search pattern in text. It is a powerful tool used in programming and text editing to find, match, validate, and manipulate strings.

How do I use this regex tester?

Simply enter your regex pattern in the 'Regular Expression' field and your test string in the text area below. The tool will instantly highlight all matches and provide a detailed breakdown of each match, including its position and any capture groups.

What are regex flags and how can I test them?

Flags modify the search behavior. Our tool supports common flags like 'g' (global search), 'i' (case-insensitive), and 'm' (multiline). You can toggle them easily in the options panel to see how they affect your pattern's matches in real-time.

What are capture groups?

A capture group, created by enclosing part of your pattern in parentheses `()`, captures the portion of the string that matches it. Our tester lists all captured groups for each match, making it easy to debug and extract specific data.

Can I use the common regex patterns provided?

Absolutely. We've included a library of common patterns for tasks like validating emails, URLs, and phone numbers. Just select one from the dropdown to load it into the tester and see how it works.

Is my data safe when using this tool?

Yes, 100%. This regex tester operates entirely in your web browser. Your regular expressions and test strings are never sent to our servers, ensuring your data remains private and secure.

How do I validate email addresses with regex?

Our tool includes a pre-built email validation pattern. Select 'Email Address' from the common patterns section to load a robust email regex. You can also customize it according to your specific requirements.

What's the difference between greedy and non-greedy quantifiers?

Greedy quantifiers (*, +, {n,m}) match as much text as possible, while non-greedy quantifiers (*?, +?, {n,m}?) match as little as possible. For example, `<.*>` matches everything between the first and last `< >`, while `<.*?>` matches each individual tag.

How can I extract specific data like phone numbers or URLs?

Use capture groups by enclosing the part you want to extract in parentheses. Our tester shows all captured groups for each match, making data extraction straightforward. Try our common patterns for phone numbers and URLs to see this in action.

Can I test multiline patterns?

Yes, enable the multiline flag (m) to make ^ and $ match the start/end of each line rather than the whole string. Also enable the 's' flag (dotAll) if you want . to match newline characters.