Regex Tester

Test and debug regular expressions with real-time pattern matching

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What is the Regex Tester?

A Regex Tester is an interactive developer tool designed to help you write, test, and debug Regular Expressions (Regex). It provides real-time pattern matching against a test string, visually highlighting captured groups and matches so you can perfect your regex syntax instantly.

JavaScript RegexPattern MatchingData Extraction

Why Test Your Regex?

  • ✓
    Avoid BugsRegex is notorious for edge cases. Test it before production.
  • ✓
    Real-time FeedbackSee exact matches and capture groups instantly.
  • ✓
    Understand SyntaxExperiment with flags like Global (g) or Multiline (m).
  • ✓
    Fast PrototypingUse our pre-built patterns to get started quickly.

How to Use

Test your regular expressions in three simple steps

01
⌨️

Write Pattern

Type your regular expression in the top input box, or select a common preset.

02
⚙️

Set Flags

Toggle flags like 'g' for global matching or 'i' for case-insensitive matching.

03
✅

Test & Debug

Paste your test string and view the highlighted matches and captured groups below.

Common Regex Uses

📝

Form Validation

Ensure user input like emails, passwords, or phone numbers are formatted correctly.

🔍

Log Parsing

Extract specific IP addresses, error codes, or timestamps from massive server logs.

🕷️

Data Scraping

Pull URLs, images, or specific HTML tags from raw web page source code.

🔄

Find & Replace

Bulk-edit text files by finding complex patterns and replacing them efficiently.

Regex Best Practices

Keep it Simple

Overly complex regex is hard to maintain. Break it down if possible.

Use Anchors

Use ^ (start) and $ (end) when validating exact string matches.

Test Edge Cases

Always test your pattern against invalid data to ensure it fails correctly.

Beware of Catastrophic Backtracking

Nested quantifiers (like (a+)+) can cause severe performance issues.

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Frequently Asked Questions

Learn more about regular expressions and pattern matching.

A regular expression is a sequence of characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation.
Flags change how the regex searches: "g" (global) finds all matches instead of stopping at the first. "i" (case-insensitive) ignores upper/lower case. "m" (multiline) makes ^ and $ match the start/end of each line. "s" (dotAll) allows the dot (.) to match newlines. "u" enables full Unicode support.
Captured groups are created by placing parts of your regex inside parentheses (). They allow you to extract specific parts of the matched string, which is extremely useful for parsing dates, URLs, or extracting specific data from a log file.
Yes! The regex matching happens entirely in your web browser using JavaScript. Your test strings and patterns are never sent to a server, making it completely safe for testing sensitive data like logs or emails.