Regex Tester
Test regular expressions with live match highlighting. Toggle g/i/m/s flags and inspect capture groups instantly — runs entirely in your browser.
About This Tool
A regular expression (regex) is a pattern language for matching text, widely used for form validation, search-and-replace, log analysis and data cleaning. QuickKit's Regex Tester lets you enter a pattern and test text and instantly highlights every match in your browser, listing capture groups for each result. No data is ever sent to a server — ideal for debugging and learning regex syntax.
Features
- ✓Live Match Highlighting — See every matching substring highlighted the moment you type a pattern and test text — no button required.
- ✓Flag Toggles — Toggle the g (global), i (case-insensitive), m (multiline) and s (dotAll) flags instantly.
- ✓Capture Group Display — Lists each match's numbered and named capture groups separately from the highlighted text.
- ✓Clear Error Messages — Shows a readable error message for invalid regex syntax instead of crashing the page.
- ✓Fully Client-Side — All matching runs in your browser. Your pattern and text are never transmitted to a server.
FAQ
- Why do I only see one match without the g flag?
- This is standard regex behavior: without the g (global) flag, the engine stops after the first match. Enable the g flag to find every match in the text.
- What are capture groups?
- Capture groups are sub-patterns wrapped in parentheses () used to extract specific parts of a match. For example, (\d{4})-(\d{2})-(\d{2}) captures year, month and day separately. This tool lists each group's captured value below every match.
- Can a complex pattern freeze my browser?
- Certain pattern structures (nested repeated quantifiers) can cause catastrophic backtracking, making the tab unresponsive for a long time. This tool caps the test text length to reduce that risk, but you should still avoid testing untrusted, complex patterns in a production context.
- Which regex syntax does this tool support?
- This tool uses the browser's native JavaScript RegExp engine directly, so it supports standard ECMAScript regex syntax including lookahead/lookbehind and named groups (subject to your browser's support level).