Regex Tester - Live Regular Expression Tester
Write a regex pattern, enter test text, and instantly see all matches highlighted with capture group details.
What Is a Regex Tester?
A regex tester lets you write regular expressions and instantly test them against sample text. This tool highlights every match in real time, shows capture groups, match indices, and supports all standard JavaScript regex flags (global, case-insensitive, multiline, dotAll). Errors are displayed immediately so you can fix syntax issues on the fly. Everything runs in your browser — no data is sent anywhere.
How to Use the Regex Tester
- Enter a Pattern — Type your regular expression in the pattern field (no delimiters needed)
- Set Flags — Toggle g (global), i (case-insensitive), m (multiline), s (dotAll) as needed
- Enter Test Text — Paste or type the text you want to match against
- View Results — Matches are highlighted instantly with count, index, and group details shown below
Why Use This Regex Tester?
- Instant Feedback — Matches update on every keystroke with zero delay
- Visual Highlighting — Matched portions are highlighted directly in the text
- Group Capture — See every capture group value for each match
- All Flags Supported — Toggle g, i, m, and s flags with checkboxes
- Error Display — Invalid regex patterns show clear error messages
- Privacy First — Runs entirely in your browser, no server processing
FreeToolbox vs Other Regex Testers
| Feature | FreeToolbox | Regex101 | RegExr |
|---|---|---|---|
| Browser-based | Yes | Server-side | Yes |
| No account needed | Yes | Optional | Yes |
| Live highlighting | Yes | Yes | Yes |
| Group capture display | Yes | Yes | Yes |
| Dark theme | Yes | Optional | No |
| No ads | Yes | No | No |
| Lightweight | Yes | Heavy | Medium |
FAQ
What regex flavor does this tool use?
This tool uses JavaScript's built-in RegExp engine. It supports all standard JavaScript regex syntax including character classes, quantifiers, lookahead, lookbehind, and named groups.
Do I need to add slashes around the pattern?
No. Just type the pattern directly. Flags are controlled by the checkboxes below the input field.
What does the 's' (dotAll) flag do?
The dotAll flag makes the dot (.) match any character including newline characters (\n, \r). Without it, the dot matches everything except newlines.
Can I test multiline patterns?
Yes. Enable the 'm' (multiline) flag to make ^ and $ match the start/end of each line instead of just the start/end of the entire string.
Is my test data stored or sent to a server?
No. Everything runs locally in your browser. Your regex pattern and test text never leave your device.