Which Regex flavor does this tester use?

This tool uses the standard ECMAScript (JavaScript) RegExp engine built into your web browser, which is directly compatible with Node.js, modern web browsers, and frontend frameworks.

How do I reference capture groups in replacement strings?

Use $1, $2, etc., to refer to parenthesized capture groups. For example, replacing '(\w+) (\w+)' with '$2, $1' inverts first and last names.

Is there any risk of ReDoS (Regular Expression Denial of Service)?

Because computation runs 100% client-side in your own browser tab, your machine is in complete control. We include automatic timeout safeguards to prevent runaway backtracking.

Regex Tester & Visualizer Online — Real-Time Matcher

About Regex Tester & Visualizer

Regex Tester & Visualizer Online

Test, debug, and validate JavaScript regular expressions with real-time pattern matching, visual capture group breakdowns, and string substitution preview.

Supported Flags

**g (Global):** Find all matches rather than stopping after the first match.

**i (Case Insensitive):** Match characters regardless of uppercase or lowercase.

**m (Multiline):** Treat beginning and end assertions (`^` and `$`) as working across each line.

**s (dotAll):** Allows `.` to match newline characters.

**u (Unicode):** Treat the pattern as a sequence of Unicode code points.

Key Features

**Real-Time Match Highlighting:** Instant visual feedback as you type your pattern or test string.

**Capturing Groups Breakdown:** View indexed capture groups (`$1`, `$2`) and named capture groups with exact string slices.

**Replacement Preview:** Test regex find-and-replace patterns interactively.

**100% Client-Side:** Evaluated directly in your browser's JavaScript V8 engine with zero data uploaded.

Supported Flags

**g (Global):** Find all matches rather than stopping after the first match.

**i (Case Insensitive):** Match characters regardless of uppercase or lowercase.

**m (Multiline):** Treat beginning and end assertions (`^` and `$`) as working across each line.

**s (dotAll):** Allows `.` to match newline characters.

**u (Unicode):** Treat the pattern as a sequence of Unicode code points.

Key Features

**Real-Time Match Highlighting:** Instant visual feedback as you type your pattern or test string.

**Capturing Groups Breakdown:** View indexed capture groups (`$1`, `$2`) and named capture groups with exact string slices.

**Replacement Preview:** Test regex find-and-replace patterns interactively.

**100% Client-Side:** Evaluated directly in your browser's JavaScript V8 engine with zero data uploaded.

Regex Tester & Visualizer

About Regex Tester & Visualizer

Regex Tester & Visualizer Online

Supported Flags

Key Features

Regex Tester & Visualizer FAQs

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Regex Tester & Visualizer

About Regex Tester & Visualizer

Regex Tester & Visualizer Online

Supported Flags

Key Features

Regex Tester & Visualizer FAQs

Related Tools

Diff & Text Compare Online

cURL to Code Converter

JSON Formatter