Regular 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.
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).
📊 Reference 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
Example 1: validate an email
Pattern: [\w.-]+@[\w.-]+\.\w{2,6} — Test on "[email protected]": full match. On "invalid-email": no match.
Example 2: extract all numbers from text
Pattern: \d+ with flag g — On "There are 3 articles and 12 categories": matches ["3", "12"].
Example 3: validate a US ZIP code
Pattern: ^\d{5}(-\d{4})?$ — On "90210": match. On "9021": no match.