Test a regex online: tool and practical guide
Test your regular expressions online with match highlighting, capturing groups and pattern explanation.
Published on January 7, 2026Regular expressions (regex) are essential in development for validating forms, extracting data, filtering logs and transforming strings. Testing a regex online lets you validate its logic instantly before integrating it into code.
Understanding the conversion
An online regex tester takes a regular expression (pattern) and an input text, then highlights all matches. It also displays capturing groups (sub-expressions in parentheses) and indicates whether the pattern is valid or contains a syntax error. Most tools support common flags: `g` (global), `i` (case-insensitive), `m` (multi-line), `s` (dotall).
📊 Conversion table
| Common pattern | Meaning | Example match |
|---|---|---|
| ^[a-zA-Z]+$ | Letters only | "Hello" |
| \d{4} | 4 consecutive digits | "2026" |
| [\w.-]+@[\w.-]+\.\w{2,} | Email address | "[email protected]" |
| https?://[\w./%-]+ | HTTP/HTTPS URL | "https://toolsmartly.com" |
| \b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b | IPv4 address | "192.168.1.1" |
💡 Practical examples
Pattern: [\w.-]+@[\w.-]+\.\w{2,6} — Test on "[email protected]": full match. On "invalid-email": no match.
Pattern: \d+ with flag g — On "There are 3 articles and 12 categories": matches ["3", "12"].
Pattern: ^\d{5}(-\d{4})?$ — On "90210": match. On "9021": no match.