Regex Tester

The Regex Tester lets you test, debug, and validate regular expressions in real-time with instant visual feedback. See matches highlighted as you type, understand what each part of your pattern does with automatic explanations, and test replacements with capture groups. Whether you're validating user input, parsing logs, or extracting data patterns, this tool helps you write better regex faster. With 13+ quick examples, a built-in cheatsheet, and code generation for JavaScript, Python, PHP, and Java, you'll master regular expressions without the frustration. All processing happens in your browser—your patterns and test data stay completely private.

How to Use

Enter your regex pattern (with or without delimiters like /pattern/flags). Toggle flags for global (g), case-insensitive (i), multiline (m), and more. Paste your test text and watch matches highlight in real-time. Check the Pattern Breakdown to understand each component. Use Find & Replace mode to test text substitutions. Generate code in your preferred language. Save frequently-used patterns to your local library for quick access.

Limitations & Important Notes

Uses JavaScript regex engine (ECMA-262). Patterns may need adjustments for Python, Java, or PCRE (PHP). Complex patterns with heavy backtracking can slow down or hang the browser. Very large texts (over 1MB) may impact performance. For production, use battle-tested validation libraries (validator.js, Joi, Yup) when possible. Regex alone can't fully validate complex formats—emails need DNS checks, dates need calendar logic.