🧪 What is this Regex Tester?

This online Regex Tester allows you to quickly test, debug, and visualize regular expressions using Java’s Pattern engine. Built with Spring Boot and Thymeleaf, it's perfect for developers working with Java regex.

Regular expressions (regex) are sequences of characters that form search patterns. They are widely used for input validation, searching, and complex string manipulation. In Java, regex is powered by the java.util.regex package.

🚀 How to Use

Choose a pattern from the dropdown or write your own regex, paste your test input, and click Run Test. You'll see both the match results and the equivalent Java code you can use.

Example: Try \\d{3}-\\d{2}-\\d{4} as a pattern and test it against 123-45-6789. The tool will highlight the match and generate the corresponding Java code snippet.

💡 Why Use This Tool?

Regex is essential for validating input, parsing logs, and text processing. This tool boosts productivity by letting you test and visualize patterns in real-time before integrating into your Java backend.

Instead of trial-and-error inside your Java IDE, you can confirm the correctness of your pattern here and instantly copy the working Java snippet. This saves time and reduces errors in production code.

📘 Regex Basics

\\d → matches any digit
\\w → matches letters, digits, or underscore
+ → one or more repetitions
* → zero or more repetitions
? → zero or one occurrence
(...) → capturing group
\\. → matches a literal dot

With these building blocks, you can create advanced patterns for emails, phone numbers, dates, or custom formats.

🧩 Java Example


import java.util.regex.*;

public class RegexExample {
    public static void main(String[] args) {
        String input = "Email: test@example.com";
        Pattern pattern = Pattern.compile("[a-zA-Z0-9._%+-]+@[a-z0-9.-]+\\.[a-z]{2,}");
        Matcher matcher = pattern.matcher(input);
        if (matcher.find()) {
            System.out.println("Found email: " + matcher.group());
        }
    }
}

Copy this snippet and replace the regex with your own. The tester below helps ensure your patterns work before pasting them into your Java application.

🔍 Regex Validation & Debugging

The tester highlights matching groups and provides clear feedback when your regex is invalid. This helps you spot missing escapes (\\) or incorrect quantifiers.

Use this tool to refine complex patterns step by step until they behave as expected.

🎯 Common Use Cases

📧 Validate email addresses
📱 Validate phone numbers
🔑 Enforce password strength rules
📄 Extract data from logs
🌍 Match URLs and domain names

These real-world scenarios are where regex truly shines in everyday development.

🌐 Regex vs Glob/Wildcards

Regex is more powerful than simple wildcards (*, ?) or file globs. While wildcards only match filename patterns, regex can match complex structures like dates, emails, and nested formats.

Example: .*\\.txt matches all .txt files but also gives you full control over prefixes/suffixes.

⚡ Performance Tips

Some regex patterns can be inefficient (catastrophic backtracking). Always test performance with large inputs.

Avoid nested quantifiers like (.+)+
Prefer non-greedy quantifiers (*?, +?) when possible
Anchor patterns with ^ and $ to reduce scanning

These tips help prevent regex from slowing down or crashing your application.

🧪 Regex Tester (Spring Boot)

✅ Match Result

🧬 Generated Java Code