Regex Tester
Test regular expressions with real-time match highlighting — supports global, case-insensitive, and multiline flags with captured group extraction.
About Regex Tester
Our free Regex Tester is a real-time regular expression testing tool that highlights matches as you type. Enter your regex pattern, set the desired flags, provide a test string, and instantly see which parts of your text match the pattern — all highlighted in the results.
The tool supports the three most common regex flags: global (g) to find all matches instead of just the first, case-insensitive (i) to match regardless of letter case, and multiline (m) to make ^ and $ match the start and end of each line rather than the entire string. Captured groups are extracted and displayed for each match.
Regular expressions are essential for text validation, search and replace operations, data extraction, and pattern matching in virtually every programming language. Common use cases include email validation, phone number parsing, URL extraction, log file analysis, and form input validation. This tool helps you build and test your patterns visually before using them in your code.
Frequently Asked Questions
Q What are regex flags?
Regex flags modify how the pattern search behaves. The "g" (global) flag finds all matches in the string rather than stopping at the first match. The "i" (case-insensitive) flag makes the pattern match both uppercase and lowercase letters. The "m" (multiline) flag changes the behavior of ^ and $ to match the start and end of each line, rather than the entire string.
Q What are capturing groups in regex?
Capturing groups are created by wrapping part of your pattern in parentheses. They "capture" the text that matches the sub-pattern within them, allowing you to extract specific parts of each match. For example, the pattern (\w+)@(\w+\.\w+) applied to "user@example.com" captures "user" in group 1 and "example.com" in group 2. Groups are numbered by their opening parenthesis from left to right.
Q What are some common regex patterns?
Some frequently used patterns include: email validation (\b[\w.-]+@[\w.-]+\.\w+\b), phone numbers (\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}), URLs (https?://[\w.-]+\.\w+[\w./-]*), dates (\d{1,2}/\d{1,2}/\d{4}), and IP addresses (\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b). These are starting points that may need adjustment for your specific requirements.