Regex Tester & Visualizer
Test Regular Expressions in real-time. Highlights matches and explains capture groups.
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/^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/gm/https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)/g/^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/gm/^(?=.*[A-Za-z])(?=.*\d)(?=.*[@$!%*#?&])[A-Za-z\d@$!%*#?&]{8,}$/g/<\/?(?:[a-z][a-z0-9]*)\b[^>]*>/giWhat is a Regex Tester?
A regex tester (regular expression tester) is a tool that lets you write, test, and debug regular expressions in real-time against sample text. It highlights all matches, shows capture groups, and helps you understand complex patterns. Regular expressions are powerful pattern-matching strings used in programming, text processing, data validation, and search operations. Our free online regex tester supports JavaScript regex syntax with flags like global (g), case-insensitive (i), and multiline (m).
How to Test Regular Expressions Online
- 1Enter your regex pattern
Type your regular expression pattern in the regex input field.
- 2Set flags
Toggle regex flags: g (global — find all matches), i (case-insensitive), m (multiline).
- 3Add test text
Paste or type the text you want to test your regex against.
- 4View matches
Matches are highlighted in real-time. Capture groups are color-coded and listed separately.
Frequently Asked Questions
Which regex flavor does this tool support?
This tool uses JavaScript's built-in RegExp engine, which supports ECMAScript regex syntax. This includes lookaheads, lookbehinds (in modern browsers), named capture groups, Unicode properties, and all standard character classes.
Can I test regex for other languages like Python or Java?
Most basic regex syntax is shared across languages. However, some advanced features (like possessive quantifiers in Java or verbose mode in Python) are language-specific. For standard patterns, JavaScript regex works as a reliable cross-language tester.
What are capture groups?
Capture groups are portions of a regex pattern enclosed in parentheses (). They "capture" the matched text so you can extract or reference it. For example, (\d{4})-(\d{2})-(\d{2}) captures year, month, and day separately from a date string.
Why Use DevDeck?
DevDeck's regex tester runs instantly in your browser with zero latency. There's no server round-trip — every keystroke updates matches in real-time. Your test data stays completely private.