About the Regex Tester Online
Test JavaScript Regular Expressions Online — Try a regular expression against sample text and highlight matches, capture groups and positions, without uploading sensitive input.
Formula or method
RegExp parses a pattern using selected JavaScript flags. The matcher highlights nonoverlapping results and reports capture groups and match indices.
Worked example
Pattern [A-Z]+\d+ matches AB123 and XY45 in the text 'Order AB123 and XY45'.
How to use the tool
- Enter a regular expression and flags.
- Paste text to test against.
- Review highlighted matches and group values.
Common uses
Developer debugging, text cleaning, validation patterns.
Assumptions and limitations
Patterns with catastrophic backtracking can block a browser despite input limits. This is not a sandbox for untrusted expressions; limits are 160-character patterns and 10,000-character text.
Frequently asked questions
What is a regex flag?
Flags such as i for case-insensitive or m for multiline change how the pattern is evaluated.
Privacy and support
Your inputs are processed locally in your browser. ToolMosaic does not upload or store the values you enter in this tool. Our tools are free, and we appreciate your support.