Regex Tester
Test regular expressions with match highlighting, capture groups, and index positions.
The Regex Tester runs a regular expression against your text with match highlighting, capture groups, and index positions. It is a hands-on way to build and debug patterns.
What is a Regex Tester?
A regex tester is a diagnostic tool that allows developers to create, validate, and debug regular expressions by applying them to sample text and visualizing the results. Regular expressions provide a powerful way to search, match, and manipulate text patterns, but they can be complex and error-prone to construct correctly. The tester provides immediate feedback by showing exactly which parts of your text match your pattern, including the positions of each match, any captured groups, and visual highlighting of the results. You enter the pattern and its flags in one field and the sample text in another, and the tool applies the expression and marks every matching span for you.
Regular expressions are fundamental to many programming tasks including form validation, data extraction, text processing, and pattern-based string manipulation. Developers across all languages use regex patterns to solve problems efficiently, but testing these patterns without proper tools often requires writing and running actual code. This tester eliminates that overhead by providing a dedicated environment where you can experiment with different patterns and flags, instantly seeing how they affect your test text. The interface supports common flags like global (g), case insensitive (i), and multiline (m) to match standard JavaScript regex behavior.
Everything runs locally in your browser using the native RegExp engine, so the patterns you test and the sample text you paste are never sent to a server or stored anywhere at all. There is no signup and no upload, which means you can iterate quickly: adjust the pattern, toggle a flag, and watch the matches and the capture groups update in the very same moment. Because the highlighting is done on the page itself, even fairly long inputs stay responsive without any network delay getting in the way. The matched spans and their capture groups can also be copied straight from the preview pane for reuse in your own code.
How to use this Regex Tester
- Enter your regular expression pattern in the regex input field, without the surrounding delimiters.
- Add optional flags (g, i, m) in the flags field to modify how the pattern is applied.
- Paste or type your test text into the test text textarea.
- Click Test to apply the regex and display all matches with their positions.
- Review the results textarea for detailed match information including indexes and capture groups.
- Use the match preview area to visually see which parts of your text are matched.
FAQ
What does the regex tester do?
The regex tester validates and tests regular expressions against provided text, showing all matches with their positions, captured groups, and visual highlighting for easy debugging.
Which flags are supported?
The tool supports the standard JavaScript RegExp flags: g (global), i (case insensitive), and m (multiline). You can combine these flags as needed for your specific pattern matching requirements.
Does it show capture groups?
Yes, when your regular expression contains capture groups using parentheses, the tool displays each captured group along with its index and position in the matched text.
Is my regex pattern stored anywhere?
No, all pattern matching and text processing occurs entirely in your browser. Your regex patterns and test text are never uploaded to any server and remain completely private.