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Regex Tester Online – Test & Debug Regular Expressions Free

Test regular expressions in real time with instant match highlighting. Supports JavaScript, Python, and Go flavors. Free regex debugger with cheat sheet included.

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About Regular Expressions

Regular expressions (regex) are powerful patterns used for matching, searching, and replacing text. They're essential for input validation, text processing, and data extraction. This tool tests your regex in real-time with JavaScript's regex engine.

Frequently Asked Questions

What is the difference between testing and matching?
Testing checks if a pattern matches a string at all (with the "g" flag, it finds all matches). Matching shows you where in the text the pattern was found and what was captured. Use tools like JSON Formatter to validate your data before testing patterns.
What do regex flags do?
The global flag (g) finds all matches; case-insensitive (i) ignores uppercase/lowercase; multiline (m) makes ^ and $ match line boundaries instead of string boundaries; dotall (s) makes . match newlines. Combine flags as needed.
How do I match email or phone numbers?
Email: /[^@]+@[^@]+\.[^@]+/. Phone (US): /\d3-\d3-\d4/. For real production use, check the validation best practices.
What's a capture group?
Parentheses in a regex create capture groups. For example, (\w+) captures one or more word characters. Groups are shown separately in the matches list, allowing you to extract specific parts of your match.
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How to Use

  1. Enter your regex pattern in the pattern field
  2. Add flags (g for global, i for case-insensitive, m for multiline)
  3. Type or paste your test text
  4. View highlighted matches and match details in real-time

Common Use Cases

  • Validating email addresses, URLs, or phone numbers
  • Extracting data from text (log parsing, web scraping)
  • Search and replace operations
  • Input validation in web forms

Frequently Asked Questions

What is a regular expression?
A regular expression (regex) is a pattern used to match, search, and manipulate text. It's supported in virtually every programming language.
How do I test my regex?
Enter your regex pattern in the pattern field, add test text below, and the tool will highlight all matches in real-time. Flags like 'g' (global) and 'i' (case-insensitive) are supported.
Is my regex data safe?
Yes. All regex processing happens in your browser using JavaScript's built-in RegExp engine. No data is sent anywhere.