What regex flags are supported?

The tester supports standard JavaScript flags: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — dot matches newlines), and u (Unicode mode).

What are capture groups in regex?

Capture groups are parts of a pattern enclosed in parentheses (). They capture the matched portion of that subpattern separately. For example, (\d{4}) captures exactly four digits as a group you can reference.

What is the difference between greedy and lazy matching?

Greedy quantifiers (*, +, ?) match as much as possible. Lazy quantifiers (*?, +?, ??) match as little as possible. Use lazy matching when you want to stop at the first available end condition.

Can I test multi-line strings?

Yes. Use the m (multiline) flag so ^ and $ match the start and end of each line rather than the entire string. Newlines can be included in the test input.

Why is my pattern matching too much of the string?

Greedy quantifiers like .* or .+ match the longest possible string. To restrict matching, use a lazy quantifier (.*? or .+?), use a character class (like [^"]*) instead of dot, or anchor the pattern with ^ and $.

Regex Tester — Test Regular Expressions Online with Live Match Highlighting

DevTool House

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regex tester

About Regex Tester

Write a regular expression and test it against any string with live match and capture group highlighting — useful for pattern matching, input validation, and text extraction.

Last reviewed

June 23, 2026

Key Features

Live match highlighting as you type the pattern
Supports all standard regex flags (g, i, m, s, u)
Shows capture groups and their matched values
Displays match count and positions
Instant feedback without page reload

How to Use Regex Tester

1Enter your regular expression in the pattern field.
2Select the flags you need (global, case-insensitive, multiline, etc.).
3Paste or type the test string to match against.
4Review highlighted matches and capture group values in the result.

Email validation pattern example

Use the pattern /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/ to test whether a string is a valid email address format. The tester highlights matches and shows immediately whether the full string passes the pattern.

How It Works

The tool evaluates the regular expression against the test string using the JavaScript regex engine, highlights all matches and capture groups, and reports match count, positions, and group values.

Privacy Notes

The pattern and test text are sent to DevTool House servers to run the match and is not stored once the result is returned. Avoid testing against text that contains passwords or personal data.

Limitations

This tester uses the JavaScript (ECMAScript) regex engine. Some patterns from Perl, Python, or PCRE flavors may use syntax not supported in JavaScript — such as variable-length lookbehind in older environments or named group syntax differences.

Frequently Asked Questions

regex tester

About Regex Tester

Write a regular expression and test it against any string with live match and capture group highlighting — useful for pattern matching, input validation, and text extraction.

Last reviewed

June 23, 2026

Key Features

Live match highlighting as you type the pattern
Supports all standard regex flags (g, i, m, s, u)
Shows capture groups and their matched values
Displays match count and positions
Instant feedback without page reload

How to Use Regex Tester

1Enter your regular expression in the pattern field.
2Select the flags you need (global, case-insensitive, multiline, etc.).
3Paste or type the test string to match against.
4Review highlighted matches and capture group values in the result.

Email validation pattern example

How It Works

The tool evaluates the regular expression against the test string using the JavaScript regex engine, highlights all matches and capture groups, and reports match count, positions, and group values.

Privacy Notes

The pattern and test text are sent to DevTool House servers to run the match and is not stored once the result is returned. Avoid testing against text that contains passwords or personal data.

Regex Tester

About Regex Tester

Key Features

How to Use Regex Tester

Email validation pattern example

How It Works

Privacy Notes

Limitations

Frequently Asked Questions

1What regex flags are supported?

2What are capture groups in regex?

3What is the difference between greedy and lazy matching?

4Can I test multi-line strings?

5Why is my pattern matching too much of the string?

Regex Tester

About Regex Tester

Key Features

How to Use Regex Tester

Email validation pattern example

How It Works

Privacy Notes

Limitations

Frequently Asked Questions

1What regex flags are supported?

2What are capture groups in regex?

3What is the difference between greedy and lazy matching?

4Can I test multi-line strings?

5Why is my pattern matching too much of the string?