Regex Tester & Debugger — Online Regular Expression Tool
Test and debug regular expressions online with real-time match highlighting and cheat sheet. 100% private.
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About Regex Tester
Regular expressions can be notoriously difficult to get right. The Tools4U Regex Tester is a high-performance debugger designed to help developers write and verify patterns with surgical precision. Our tool features real-time match highlighting, support for global flags (g, i, m, s), and an integrated cheat sheet for quick syntax reference. You can test your patterns against multi-line strings and see exactly what is being captured in groups. Because privacy is our priority, your regex strings and test data are processed entirely in your browser and never touch our servers.
Build patterns with confidence, debug with precision.
Core Features
- Real-time Matching: Highlights update instantly as you refine your regex pattern.
- Group Capturing: Detailed breakdown of capturing groups and their positions.
- Native Engine: Uses standard JavaScript RegExp logic for 100% web compatibility.
- Flags Control: Easily toggle Global, Case-Insensitive, Multi-line, and Dot-all modes.
- Integrated Cheat Sheet: Quick reference for anchors, quantifiers, and character classes.
- Privacy First: All debugging happens locally. We never see your code or test data.
How to Use Regex Tester
Enter your regular expression pattern in the top input box (between the slashes).
Toggle any required flags (like 'g' for global or 'i' for case-insensitive).
Paste your test data into the large text area below.
Review the highlighted matches and the detailed results list in the sidebar.
Use the 'Copy' icon to save your finished /pattern/flags to your project.
Who Uses Regex Tester
Form Validation
Test email, phone number, and password patterns before implementing them in your frontend or backend code.
Log Scraping
Quickly build patterns to extract specific identifiers, dates, or error codes from messy server logs.
Data Cleanup
Verify search-and-replace patterns to ensure you aren't accidentally removing required text segments.
Learning Regex
Use the live feedback and cheat sheet to understand how different tokens interact with sample text.