Regex Tester
Test regular expressions with live matching and capture groups
Enter a pattern and test string to start matching
Uses the JavaScript RegExp engine. All processing happens locally in your browser.
About Regex Tester
Test and debug regular expressions with live matching, capture group highlighting, and flag support. Regular expressions are a powerful pattern-matching language used for text search, validation, extraction, and replacement in virtually every programming language. This tester uses the browser JavaScript RegExp engine, giving you accurate results for patterns you will use in frontend and Node.js code. Matches are highlighted in real time as you type, and capture groups are displayed in a structured table. The regex runs in a Web Worker to avoid blocking the page on complex patterns.
How to Use Regex Tester
- Enter your regular expression pattern in the pattern field.
- Set flags (g, i, m, s, u) using the flag toggles.
- Type or paste test text in the input area.
- View highlighted matches and capture group details in real time.
Regex Tester FAQ
Which regex engine is used?
The tool uses the browser JavaScript RegExp engine, so pattern behaviour matches what you get in frontend JavaScript and Node.js.
Can I test capture groups and flags?
Yes. The tester displays all capture groups (numbered and named) in a structured table and supports standard flags: global (g), case-insensitive (i), multiline (m), dotAll (s), and unicode (u).
Will complex patterns freeze the page?
No. Regex execution runs in a Web Worker, so even complex or pathological patterns will not block the UI. Execution is automatically terminated if it exceeds time limits.
Can I use this to test regex for other languages?
The tool uses JavaScript regex syntax, which is largely compatible with other languages. However, features like lookbehinds, possessive quantifiers, and atomic groups vary between engines.
What are common use cases for regex?
Regular expressions are used for form validation, log parsing, search-and-replace in editors, URL routing, data extraction from text, and input sanitisation in applications.