Online Regex Tester — Test and Debug Regular Expressions in Real Time

Our free online regex tester lets you write, test and debug regular expressions instantly against any test string. See all matches highlighted with capture group details — no page reloads, no installation required. Supports JavaScript regex syntax including global (g), case-insensitive (i) and multiline (m) flags.

Essential Regular Expression Patterns for IT Professionals

• IPv4 Address: (\d{1,3}\.){3}\d{1,3}
• Email Address: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
• URL: https?://[^\s/$.?#].[^\s]*
• MAC Address: ([0-9A-Fa-f]{2}[:-]){5}[0-9A-Fa-f]{2}
• UK Postcode: [A-Z]{1,2}\d[A-Z\d]? ?\d[A-Z]{2}
• ISO Date (YYYY-MM-DD): \d{4}-\d{2}-\d{2}
• Log timestamp: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}
• CIDR Notation: \d{1,3}(\.\d{1,3}){3}\/\d{1,2}

Regex Flags Explained

• g (global) — finds all matches in the string rather than stopping at the first
• i (case insensitive) — matches uppercase and lowercase equally
• m (multiline) — makes ^ and $ match the start and end of each line, not just the whole string

Common Regex Use Cases in IT

Regular expressions are used throughout IT: log file parsing to extract IP addresses, timestamps and error codes; input validation in web applications; grep and sed commands in Linux shell scripting; firewall log analysis; CI/CD pipelines for parsing build output; and SIEM tools for pattern matching on security events.