Regex Tester & Debugger
This tool allows you to write, test, and debug regular expressions against custom text with live syntax highlighting and match group extraction.
Common Patterns
What is Regex Tester & Debugger?
A Regular Expression (Regex) is a sequence of characters that specifies a search pattern in text. It is widely used in string searching algorithms for "find" or "find and replace" operations, or for input validation. A Regex Tester provides a visual interface to see exactly how your regex engine evaluates a pattern against a test string, highlighting capture groups, boundaries, and matches in real-time. This tool uses the native JavaScript regex engine (ECMAScript flavor).
How to use Regex Tester & Debugger
- Enter your regular expression in the Regex input field at the top.
- Toggle flags like global (g), case-insensitive (i), or multiline (m) as needed.
- Paste your test text into the Test String textarea.
- Matches and capture groups will be highlighted live in the text.
- Check the results panel to see detailed match indexes and extracted strings.
Regex Tester & Debugger Example
Regex: /b[aeiou]g/g Text: The big bug in the bag.
Matches: big, bug, bag
Frequently Asked Questions
What regex flavor does this tool use?
This tool uses the native JavaScript (ECMAScript) regex engine built into your browser. It supports features like lookaheads and lookbehinds depending on your browser version.
Are my regex patterns saved or uploaded?
No, all testing happens purely locally in your browser. Nothing is sent to our servers.
How do I extract specific parts of a match?
Use capture groups by wrapping parts of your regex in parentheses (). The results panel will break down each match and display its extracted groups.
Why is my regex hanging or crashing?
You may be experiencing 'catastrophic backtracking' caused by nested quantifiers (like (a+)+) on long failing strings. Always write precise patterns and avoid overlapping quantifiers.
Can I use PCRE specific syntax here?
Since this uses the JS regex engine, PCRE-only features (like recursive patterns or possessive quantifiers) are not supported.