Regex101

Test regular expressions in real-time with match highlighting, explanation, and debugging tools.

Regular Expression

Test String

Case-Insensitive (i flag)

Result

Please check your inputs.

Enter your regex pattern in the 'Regular Expression' field at the top of the page. Type or paste your test string into the large 'Test String' box below. Watch real-time match highlighting appear in the test string, and read the detailed explanation panel on the right for each regex component. Enable the 'Debugger' tab to step through the regex engine's matching process character by character. Use the 'Save & Share' button to generate a unique link that you can bookmark or send to collaborate.

📖 How to Use This Tool

Enter your regex pattern in the 'Regular Expression' field at the top of the page.

Type or paste your test string into the large 'Test String' box below.

Watch real-time match highlighting appear in the test string, and read the detailed explanation panel on the right for each regex component.

Enable the 'Debugger' tab to step through the regex engine's matching process character by character.

Use the 'Save & Share' button to generate a unique link that you can bookmark or send to collaborate.

📝 What Is Regex101?

Regex101 is an interactive online tool designed to help developers test, debug, and understand regular expressions in real time. Instead of blindly writing complex patterns and hoping they work, you can instantly see which parts of your test string match, get a plain‑English breakdown of each regex element, and even walk through the engine’s logic step by step. This matters because regular expressions are notoriously hard to get right — a single misplaced character can break an entire validation or search. Regex101 eliminates guesswork by providing immediate visual feedback and educational explanations, making it an essential companion for anyone who works with pattern matching in programming, data parsing, or text processing.

🧮 Formula

The core formula is the regex pattern itself, written as /pattern/flags. The pattern is a sequence of literal characters (e.g., 'abc') and metacharacters (e.g., . * + ? [ ] ( ) | ^ $) that define a search rule. Flags modify the pattern's behavior: g (global match all), i (case‑insensitive), m (multiline anchors), s (dotall), and others. The tool applies this pattern against the test string using the selected engine (PCRE, ECMAScript, Python, Golang) and highlights all matches while explaining each part in plain language.

💡 Tips for Best Results

✨🧪 Use the 'Quick Reference' panel on the right to learn regex syntax and common patterns without leaving the tool.

✨🔍 Enable the 'Debugger' mode when a pattern doesn’t match — it shows exactly how the engine moves through the string, revealing why certain parts fail.

✨🚀 Always test with edge cases like empty strings, repeated characters, and special characters to ensure your regex handles real‑world input.

✨💡 Save your regexes using the unique link and share them with teammates to collaborate on complex patterns or document solutions.

❓ Frequently Asked Questions

Is Regex101 free to use?

Yes, Regex101 is completely free and does not require any registration. You can start testing, saving, and sharing regexes immediately.

Which regex flavors does Regex101 support?

Regex101 supports PCRE (PHP), ECMAScript (JavaScript), Python, and Golang regex engines. You can switch between them from the dropdown menu at the top.

Can I use Regex101 offline?

No, Regex101 is a web‑based tool that requires an active internet connection. However, you can save your patterns online and access them later via share links.