Regex Tester
Free online regex tester — test and debug regular expressions with real-time matching, highlighting, and capture group display. Alternative to RegExr.
About Regex Tester
A free online regex tester and regular expression debugger. Paste your regex pattern and test string to see real-time match highlighting, capture groups, and flag results. Supports JavaScript regexp syntax with all flags — global (g), case-insensitive (i), multiline (m), dotAll (s), and unicode (u). Use it to build, test, and debug regular expressions interactively. View all matches with named and numbered capture groups, test replacement patterns, and get instant feedback as you type. Works as a powerful alternative to RegExr and other regex online tools. Whether you're writing a regex for validation, parsing, or search-and-replace — test it here instantly, 100% in your browser.
Key Features
- Process and analyze data entirely in your browser — nothing is sent to any server
- Handles edge cases, special characters, and large inputs gracefully
- Real-time matching and highlighting as you type
- Support for multiple regex flags (g, i, m, s)
- Visual breakdown of match groups and captures
- Responsive design — works perfectly on desktop, tablet, and mobile
How to Use Regex Tester
- 1Enter your regular expression pattern in the pattern field
- 2Set the flags you need (global, case-insensitive, multiline, etc.)
- 3Paste your test string in the text area below
- 4View highlighted matches and captured groups in real time
When to Use Regex Tester
Regex Tester is ideal for developers who need a quick, reliable way to free online regex tester — test and debug regular expressions with real-time matching, highlighting, and capture group display. alternative to regexr. Whether you're working on a personal project, debugging production issues, or building enterprise applications, this tool saves time by handling dev utilities tasks directly in your browser without requiring any software installation or account setup.
Common use cases include day-to-day development workflows, code reviews, API debugging, data migration tasks, and quick one-off transformations. Since all processing happens client-side, Regex Tester is safe to use with sensitive or proprietary data — nothing ever leaves your machine.
Frequently Asked Questions
Q.What is regex (regular expression)?
A regex (regular expression) is a pattern used to match, search, and manipulate text. Regular expressions are used in programming, text editors, and command-line tools for tasks like validation, parsing, and find-and-replace operations.
Q.How do I test a regex online?
Enter your regex pattern in the top field and your test string below. Matches are highlighted in real-time as you type. All capture groups, match indexes, and flag results are displayed instantly.
Q.Which regex flavor is used?
The tool uses JavaScript's built-in RegExp engine, which supports most common regex features including lookaheads, lookbehinds, named capture groups, and unicode properties.
Q.How is this different from RegExr?
This regex tester runs 100% in your browser with no signup or tracking. It provides the same real-time regex matching and highlighting as RegExr, plus capture group display and flag toggling — all in a clean, distraction-free interface.
Q.Can I see capture groups?
Yes. All matched groups — both numbered and named capture groups — are displayed with their values for each match, making it easy to debug complex regular expressions.
Q.Which flags are supported?
Global (g), case-insensitive (i), multiline (m), dotAll (s), unicode (u), and sticky (y) flags are all supported. Toggle them with a single click.
Related Articles
Regex Cheat Sheet for Developers — Patterns, Flags & Examples
A practical regex reference with common patterns, flags, lookaheads, and real-world examples for JavaScript, Python, and more.
Cron Expressions Explained — Syntax, Examples & Common Schedules
Learn cron expression syntax from scratch — fields, wildcards, ranges, steps, and ready-to-use examples for common schedules.
Related Tools
Text Diff Checker
Free online diff checker — compare text online side-by-side and highlight every difference. Fast text compare tool and DiffChecker alternative.
Word & Character Counter
Count words, characters, sentences, paragraphs, and estimate reading time.
Case Converter
Convert text between uppercase, lowercase, title case, camelCase, snake_case, and more.
Line Sorter & Deduplicator
Sort lines alphabetically, reverse order, remove duplicates, and trim blank lines.