RegEx Tester
Test and debug regular expressions with live matches.
100% Private & Client-Side Execution
Patterns and test strings remain entirely on your device with zero remote server logging.
About RegEx Tester
RegEx Tester is an interactive debugging sandbox for JavaScript regular expressions. It provides instant visual match highlighting, capture group inspection, and flag toggling (global, case-insensitive, multiline), helping developers write and test patterns before deploying them to production.
How to Use RegEx Tester
- Enter your regular expression pattern in the Pattern input box (e.g. `[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}`).
- Toggle active regex flags: "g" (global), "i" (case-insensitive), or "m" (multiline).
- Type or paste your test text into the Test String workspace.
- Examine the highlighted match badges, match indices, and numbered capture groups updating in real time.
- Review any regex syntax error notifications to correct invalid patterns immediately.
Common Real-World Use Cases
- Backend Developers: Test email, phone number, and password validation regex rules before adding them to server controllers.
- Data Cleaners: Construct regex search patterns to find and extract structured data from unstructured text logs.
- Frontend Engineers: Verify client-side form input validation patterns for HTML5 forms.
- Students & Learners: Experiment with character classes, lookaheads, quantifiers, and capture groups interactively.
Technical Specifications & Limitations
Runs using the browser's native JavaScript ECMAScript RegExp engine with built-in regex timeout protection.
Frequently Asked Questions
- What do common RegEx flags like "g", "i", and "m" do?
- "g" (global) finds all matches rather than stopping at the first; "i" ignores uppercase/lowercase distinctions; "m" treats each line as a new line for ^ and $ anchors.
- Does this tester support capture groups?
- Yes. Any patterns wrapped in parentheses `(...)` create numbered capture groups that are extracted and displayed in the match inspector.
- Which RegEx engine does this tool use?
- It uses your browser's native V8/SpiderMonkey JavaScript RegExp engine, ensuring 100% compatibility with JavaScript, TypeScript, and Node.js code.
- How can I prevent catastrophic backtracking in regular expressions?
- Avoid nesting ambiguous quantifiers like `(a+)+` which cause exponential CPU consumption when evaluating non-matching strings.
- Is my test text uploaded anywhere?
- No. Regex evaluation runs in a secure client-side sandbox inside your local browser session.