Regex Tester
Test regular expressions with live match highlighting, flag support, and capture group display.
About Regex Tester
This free online regular expression tester lets you write, test, and debug regex patterns in real time. Matches are highlighted instantly as you type, with full support for global, case-insensitive, and multiline flags. All processing happens entirely in your browser — no data is sent to any server.
How to Use
- Enter your regular expression pattern in the input field.
- Toggle the flags you need: g (global), i (case insensitive), or m (multiline).
- Type or paste your test string in the textarea below. Matches are highlighted in real time.
- Review the match details section for index positions and capture group values.
Frequently Asked Questions
What is a regular expression?
A regular expression (regex) is a sequence of characters that defines a search pattern. It is used for pattern matching within strings, commonly for validation, searching, and text manipulation in programming.
What do the flags g, i, and m mean?
The g (global) flag finds all matches rather than stopping after the first. The i (case insensitive) flag makes the pattern match regardless of letter case. The m (multiline) flag makes ^ and $ match the start and end of each line instead of the whole string.
What are capture groups?
Capture groups are portions of a regex pattern enclosed in parentheses (). They extract specific parts of a match. For example, the pattern (\w+)@(\w+) has two capture groups that extract the username and domain from an email address.
Is my data sent to a server?
No. All regex processing happens entirely in your browser using JavaScript. No data is transmitted to any external server.