Regex Tester — Quick Guide

Test and debug JavaScript regular expressions (regex) quickly and safely in your browser. This tool helps you visualize matches, capture groups, and flags without sending any data to a server.

How to use the JavaScript Regex Tester

1. Enter your regex pattern in the first input field.
2. Enter the test string in the second input field.
3. Click Test to see matches, captured groups, and replacement results if applicable.
4. Optionally, toggle regex flags like g, i, or m.
5. Open the Regex Tester

Example

Pattern: (\w+)@(\w+)\.(\w+)
Test string: user@example.com

Matches

Full match: user@example.com
Group 1: user
Group 2: example
Group 3: com

Best practices

• Escape special characters: Use backslashes \ for characters like . or *.
• Use flags wisely: g for global, i for case-insensitive, m for multiline.
• Test edge cases: Regex can behave differently for empty strings or unexpected input.
• Use capture groups thoughtfully: Avoid unnecessary groups to simplify your matches.
• Performance matters: Complex regex patterns can slow down execution on large strings.

Common pitfalls

• Forgetting to escape regex special characters.
• Misunderstanding greedy vs. lazy quantifiers (* vs. *?).
• Overlooking multiline matches when ^ and $ are used.

FAQs

Does this tool send my data to a server?

No. All regex testing happens locally in your browser, keeping your data private.

Can I use it for large text?

Yes, but extremely large strings may slow down your browser due to regex evaluation.

Does it support all JavaScript regex features?

It supports standard JavaScript regex syntax including lookaheads, lookbehinds, capture groups, and flags.

Try it now: JavaScript Regex Tester