Regex tester

Free Online Regex Tool with JS & PCRE Support

Use our free online regex tester to build, test, and debug regular expressions fast. Paste a test string, pick your flavor (JavaScript or PCRE), and see instant matches, groups, and replacements—no sign-up, no uploads, no tracking. The regular expression tester runs 100% in your browser for privacy and speed. Not sure what a pattern does? Turn on 'Explain this regex' to see a human-readable breakdown. Start with the examples below or craft your own pattern in seconds.

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Instant Results

Live match, groups, and replace previews as you type.

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Explain this regex

One-click breakdown of tokens, anchors, groups, and quantifiers.

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Multiple Flavors

JavaScript and PCRE regex engine support

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Private by design

100% client-side; this regex builder sends nothing over the network.

Regular Expression Pattern:

Flavor:

Explain this regex

Flags:

g (global)i (case insensitive)m (multiline)

Test Strings

Test String 1:

Common Use Cases

Email Validation

Use when: Validating email addresses in forms, user registration, or contact information processing.

^[^\s@]+@[^\s@]+\.[^\s@]+$

Test strings: user@example.com ✓, invalid-email ✗

Phone Number Extraction

Use when: Extract phone numbers from text in various US formats including parentheses, dots, and dashes.

\(?(\d3)\)?[-.\\s]?(\d3)[-.\\s]?(\d4)

Test strings: (555) 123-4567 ✓, 555.123.4567 ✓, 555 123 4567 ✓

URL Detection

Use when: Extracting URLs from text content, validating links, or parsing web content for hyperlinks.

^https?:\/\/[^\s/$.?#].[^\s]*$

Test strings: https://example.com ✓, http://subdomain.site.org/path ✓

UUID v4 (Case-Insensitive)

Use when: Validating unique identifiers in APIs, databases, or tracking systems that use UUID v4 format.

^[0-9a-f]8-[0-9a-f]4-4[0-9a-f]3-[89ab][0-9a-f]3-[0-9a-f]12$

Test strings: 550e8400-e29b-41d4-a716-446655440000 ✓

IPv4 Address

Use when: Validating IP addresses in network configurations, server logs, or security monitoring systems.

^((25[0-5]|2[0-4]\d|1\d2|[1-9]?\d)\.)3(25[0-5]|2[0-4]\d|1\d2|[1-9]?\d)$

Test strings: 192.168.1.1 ✓, 256.1.1.1 ✗

Hex Color Code

Use when: Parsing CSS files, validating color inputs in design tools, or extracting colors from stylesheets.

^#(?:[0-9a-fA-F]3|[0-9a-fA-F]6)$

Test strings: #FF0000 ✓, #F00 ✓, #GGG ✗

URL Slug

Use when: Validating URL-friendly identifiers for blog posts, product pages, or any web content requiring clean URLs.

^[a-z0-9]+(?:-[a-z0-9]+)*$

Test strings: my-awesome-post ✓, invalid_slug ✗

Perfect for Modern Builders

Developers

Debug regex patterns for form validation and data parsing

💡 Validate email addresses in user registration forms

AI Builders

Test patterns for data extraction and prompt engineering

💡 Extract structured data from AI model responses

Data Analysts

Extract structured data from unformatted text files

💡 Parse log files to extract error patterns and timestamps

How It Works

Step-by-Step Process

1Enter the text you want to match against

2Create your regex pattern with visual feedback

3Select JavaScript or PCRE engine

4Verify matches and copy your pattern

Regex Fundamentals & Common Patterns

Basic Patterns: Use . for any character, * for zero or more, + for one or more, and ? for optional. Combine with character classes like [a-z] or [0-9].
Anchors & Boundaries: Use ^ for start of line, $ for end of line, and \b for word boundaries. These ensure your pattern matches exactly where you expect.
Capture Groups: Use parentheses () to capture parts of your match. Access captured groups in replacements or use (?:...) for non-capturing groups to group without capturing.
Common Gotchas: Escape special characters with backslash \. Remember that .* is greedy (matches as much as possible) - use .*? for non-greedy matching.
Testing Strategy: Always test with edge cases: empty strings, very long strings, and strings that almost match. Use multiple test cases to ensure your pattern works reliably.

Frequently Asked Questions

What is a regex tester?

A regex tester (regular expression tester) lets you build, run, and debug patterns against sample text. This online regex tester shows matches, capture groups, and replacements in real time.

How do I test regex online?

Paste your text, type a pattern, pick flags like g, i, or m, and select JavaScript or PCRE flavor. Results update instantly, and you can copy the final pattern and flags.

What's the difference between JavaScript and PCRE regex?

JavaScript regex follows the ECMAScript spec and runs in browsers/Node.js. PCRE supports additional tokens and lookbehinds in many server tools. Use the flavor picker to switch behavior.

Can this tool explain a regex?

Yes. Toggle "Explain this regex" to see a human-readable breakdown of anchors, character classes, groups, and quantifiers—great for learning and code reviews.

Why does my regex not match?

Common issues include missing anchors (^/$), forgetting global g for multiple matches, escaping special characters, or using a token that's not supported by your chosen flavor.

Is this regex tester private?

Yes. The tool runs entirely in your browser and does not upload your text or patterns. There's no tracking, no ads, and no sign-ups.