Is Regex Tester free?

Yes, completely free with unlimited tests, no registration, and no ads. All features are available to everyone at no cost.

What regex engines does Regex Tester support?

Regex Tester uses JavaScript's native RegExp engine (ECMAScript 2024). It supports all standard features including lookahead, lookbehind, named capture groups, and Unicode properties.

Can I test multiline regex patterns?

Yes. Enable the 'm' (multiline) flag to make ^ and $ match line boundaries instead of just string boundaries. Paste multiline text in the test string field and matches will highlight across all lines.

What do the different flags mean in Regex Tester?

'g' finds all matches (not just the first), 'i' ignores case, 'm' treats ^ and $ as line anchors, 's' makes . match newlines, 'u' enables Unicode matching, and 'y' enables sticky mode matching.

How do capture groups work in Regex Tester?

Capture groups are subexpressions in parentheses. Regex Tester displays each group's matched text, index position, and length in the Capture Groups table. Group 0 is always the full match; Group 1+ are parenthesized patterns.

Is my regex pattern data secure?

Yes. All processing happens entirely in your browser using JavaScript. Your patterns and test strings never leave your device or connect to external servers.

Does Regex Tester work on mobile devices?

Yes, fully responsive. Works on iPhone, Android, iPad, and desktop browsers. The interface adapts to smaller screens with stacked panels and touch-friendly controls.

Can I export or save my regex tests?

Yes. Click 'Export' to download your pattern and test string as a .json file, or click 'Copy' to copy the shareable URL containing your regex and test data to clipboard.

What happens if my regex has a syntax error?

Regex Tester displays a red error message below the pattern field explaining the error type and character position. Common errors include unmatched brackets, invalid escape sequences, and malformed quantifiers.

Can I test lookahead and lookbehind assertions?

Yes. Regex Tester fully supports positive lookahead (?=...), negative lookahead (?!...), positive lookbehind (?<=...), and negative lookbehind (?<!...) assertions in your patterns.

capture groups

Regex Tester — capture groups

Test and debug regular expressions online. Highlight matches, test flags, and view capture groups.

Regular expression

//g

Flags

Test string

How to use Regex Tester

Enter Your Regular Expression

Click the 'Pattern' input field at the top of the editor. Type or paste your regex pattern (e.g., ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$). The pattern box accepts all standard regex syntax including anchors, character classes, and quantifiers.

Input Text to Test Against

Click the 'Test String' textarea below the pattern field. Paste or type the text you want to match against your regex. You can test multiple lines by pressing Enter. The tool will immediately process and display results in real-time.

Select Regex Flags

Check the flag checkboxes on the right side: 'g' (global - find all matches), 'i' (case-insensitive), 'm' (multiline), 's' (dotall), 'u' (unicode). Selected flags will modify how your pattern matches. The interface shows which flags are currently active in green.

Review Highlighted Matches

View the test string area where all matches are highlighted in yellow or blue. Each match is numbered sequentially. Hover over highlighted text to see the exact character position and matched content in the tooltip.

Examine Capture Groups

Scroll to the 'Capture Groups' panel below the text area. This table shows all matched groups with their content, position, and length. Each row represents one captured group (Group 0 is the full match, Group 1+ are parenthesized subexpressions).

Check Match Count and Details

View the 'Results' summary box showing total matches found, execution time, and any regex errors. If your pattern has syntax errors, the error message appears in red text explaining the issue and line number.

Frequently Asked Questions

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