Regex Tester
Test and debug regular expressions in real time. See matches highlighted, capture groups extracted, and flags applied. Supports JavaScript regex syntax. Free.
No sign-up
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100% free
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Private
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Pattern
Use $1, $2, etc. for capture group backreferences
Pattern Explanation
Match Details
Replacement Result
Validation
Extraction
Text
Cheat Sheet
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Online Regular Expression Tester
The Online Regular Expression Tester is a free browser-based tool that lets you write, test, and debug regular expressions (regex) in real time. Enter your regex pattern and test string, and the tool instantly highlights all matches, shows captured groups, and provides detailed match information including position, length, and group contents. The tool supports JavaScript, Python, and PCRE regex flavors with all common flags (global, case-insensitive, multiline, dotall, unicode).The interface features a pattern input with syntax highlighting, a test string area where matches are highlighted in real time as you type, a match details panel showing each match with its captured groups, and a quick reference sidebar with common regex tokens and examples. You can toggle flags (g, i, m, s, u) with checkboxes and see how each flag affects matching behavior instantly. The tool also provides the regex as a ready-to-use code snippet for JavaScript, Python, Java, and C#.Developers debug complex patterns for input validation, data extraction, and text processing. Data engineers craft patterns for log parsing, ETL pipelines, and data cleaning. DevOps engineers write patterns for log monitoring rules and alert conditions. QA testers verify that validation patterns match expected inputs and reject invalid ones. Students learning regex experiment with patterns and see immediate visual feedback. The real-time highlighting makes it dramatically faster to develop correct patterns compared to compile-and-run cycles.Regex Tester is part of the facilita.tools developer toolkit. Available in Portuguese, English, and Spanish, optimized for desktop and mobile browsers.
Frequently Asked Questions
What is a regular expression (regex)?
A regular expression is a pattern that describes a set of strings. It is used for searching, matching, and manipulating text. Common uses include email validation, phone number extraction, and log file parsing.
What do the regex flags (g, i, m) mean?
The 'g' flag enables global matching (find all matches, not just the first). The 'i' flag makes the pattern case-insensitive. The 'm' flag enables multiline mode where ^ and $ match line boundaries instead of string boundaries.
How do I match an email address with regex?
A basic email regex pattern is: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}. However, fully RFC-compliant email validation is extremely complex. For production use, combine a simple regex with server-side validation.