Regex Tester
Test and debug regular expressions with real-time matching, capture groups, and highlighted results.
//g
Enter a pattern to see results.
How to Test Regular Expressions
- 1Enter your regular expression pattern in the pattern input field at the top.
- 2Toggle regex flags (g, i, m, s) using the flag buttons to control matching behavior.
- 3Type or paste your test string in the text area below.
- 4Matches are highlighted in real time. View match details including index and capture groups in the results panel.
- 5Use the Common Patterns section for quick access to frequently used regex patterns like email, URL, or IP address.
Features
●Real-time regex matching with instant highlighting
●Support for global, case-insensitive, multiline, and dotAll flags
●Capture group extraction with numbered and named groups
●Match index positions for precise debugging
●Built-in common regex patterns library for quick reference
●Invalid pattern detection with clear error messages
●100% client-side — your test data never leaves your browser
●Free to use with no limitations or sign-up
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 in programming for string matching, validation, search-and-replace, and text parsing. For example, the regex \d+ matches one or more digits. Regex is supported in virtually all programming languages including JavaScript, Python, Java, and Go.
What do the regex flags (g, i, m, s) mean?▼
The 'g' (global) flag finds all matches instead of stopping at the first one. The 'i' (case-insensitive) flag ignores letter casing. The 'm' (multiline) flag makes ^ and $ match the start and end of each line. The 's' (dotAll) flag makes the dot (.) match newline characters as well.
What are capture groups?▼
Capture groups are portions of a regex pattern enclosed in parentheses (). They extract specific parts of a match. For example, in the pattern (\d{4})-(\d{2})-(\d{2}) matching '2024-01-15', group 1 captures '2024', group 2 captures '01', and group 3 captures '15'. Named groups use (?<name>...) syntax.
Why is my regex not matching?▼
Common issues include: forgetting the 'g' flag for multiple matches, not escaping special characters (like . or *), incorrect anchoring with ^ and $, or case sensitivity (try the 'i' flag). This tool highlights matches in real time, so you can iterate quickly to debug your pattern.
Is my test data safe?▼
Yes. All regex matching is performed entirely in your browser using JavaScript's native RegExp engine. No data is transmitted to any server. Your patterns and test strings remain completely private.
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