Regex Tester & Pattern Validator

Regular Expressions Explained

Regular expressions (regex) are patterns that describe text. They're essential for search, validation, and text manipulation in programming. While powerful, regex syntax is notoriously cryptic—interactive testing makes pattern development much faster.

Common Regex Use Cases

Validation: Check if input matches expected formats—email addresses, phone numbers, URLs, postal codes. Regex provides flexible pattern matching that handles variations.

Search and extraction: Find specific patterns in text, extract data from logs, parse structured content. Capture groups let you extract specific portions of matches.

Find and replace: Transform text by matching patterns and substituting replacements. Capture group references allow complex transformations.

Regex Dialects

Different programming languages implement regex slightly differently. JavaScript (used by our tester) has specific behaviors around flags, lookahead/lookbehind support, and Unicode handling. Test patterns in the target language when precision matters.

Testing Best Practices

• Start simple and build complexity incrementally
• Test with edge cases: empty strings, special characters, very long input
• Use capture groups to verify you're matching the right portions
• Consider performance—backtracking can cause exponential slowdowns

Common Patterns

Email: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}

URL: https?://[^\s]+

Phone (US): \(?\d{3}\)?[-\s.]?\d{3}[-\s.]?\d{4}