Regex Tester
Test regular expressions against sample text with live match highlighting, capture groups, and flag toggles. Everything runs locally in your browser using JavaScript's native regex engine.
Flags
Common Patterns
About Regex Tester
Regex Tester is a free online tool for building and debugging regular expressions using JavaScript's native RegExp engine. Type a pattern and a sample string to see every match highlighted directly in the text, with a detailed breakdown of each match's position and capture groups.
Because it runs the exact same RegExp implementation used in browsers and Node.js, patterns you validate here behave identically once copied into your codebase. It is a practical javascript regex debugger for form validation, log parsing, and text extraction tasks.
How to Use the Regex Tester
- Type or paste a regular expression pattern into the Regular Expression field.
- Toggle the g, i, m, s, u, and y flags to match your intended behavior.
- Paste a test string below and watch matches highlight live as you type.
- Review the Matches panel for each match's index and any numbered or named capture groups.
Built for Fast Iteration
Live Match Highlighter
See exactly what your pattern matches inside real text as you refine it, no need to run code to check.
Capture Group Clarity
Numbered and named groups are listed separately for every match, making extraction logic easy to verify.
Who Should Use This Tool
- Frontend Developers validating form inputs like emails, phone numbers, and passwords.
- Backend Developers parsing log lines or extracting structured data from raw text.
- QA Engineers confirming validation rules match every intended edge case.
- Students and Learners experimenting with regex syntax and flag behavior interactively.
Privacy First
Your pattern and test string are never uploaded or sent to a server. All matching happens locally in your browser using JavaScript's built-in RegExp engine, so text you paste, sensitive or otherwise, stays on your device.