Regex Check Online — Regular Expression Tester & Debugger

Free regex check online tool with real-time match highlighting, capture group inspection, and flag support. Test JavaScript regex, Ruby regex patterns, and more — paste your pattern and test string to see matches instantly.

Regex Tester: Use this regex check online tool to enter a regex pattern and test string — see matches highlighted instantly. Supports JavaScript regex syntax with flags (g, i, m, s). Also useful as a Ruby regex test tool since most basic patterns are cross-compatible. View capture groups, match indices, and replacement results.

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Key Takeaways

Real-time match highlighting as you type the pattern
Supports JavaScript regex flags: global (g), case-insensitive (i), multiline (m)
Shows numbered capture groups and named groups
Test replacement patterns with $1, $2 backreferences
Common patterns: email, URL, phone, IP address, date formats

What is Regex Tester?

Regex Tester — A regex check online tool (regex tester) is a free utility that lets you write, test, and debug regular expressions against sample text with real-time match highlighting. Works for JavaScript, Ruby regex test, Python, and other flavors.

Regex check online — test and debug regular expressions with this free regex tester. Enter your regex pattern and test string to see matches highlighted in real time as you type. The tool supports JavaScript regex syntax with all flags — global (g), case-insensitive (i), multiline (m), dotAll (s), and unicode (u). Also works as a Ruby regex test tool since most standard regex patterns (character classes, quantifiers, anchors, groups) are compatible across JavaScript and Ruby. Inspect numbered and named capture groups, view match indices, and test replacement patterns with backreferences ($1, $2). Useful for building form validation rules, log parsing patterns, text extraction logic, and search-and-replace operations before adding them to your code.

How to Use Regex Tester

1
Enter your regular expression pattern in the regex input field.
2
Paste or type the test string you want to match against.
3
Toggle regex flags (global, case-insensitive, multiline) as needed.
4
Review highlighted matches, capture groups, and match indices — refine your pattern until it works correctly.

Key Features

Real-time match highlighting as you type the pattern

Full JavaScript regex flag support: g, i, m, s, u, y

Numbered and named capture group inspection

Match index positions shown for each match

Replacement pattern testing with $1, $2 backreferences

100% client-side — no data sent to any server

Use Cases

Build and test form validation patterns (email, phone, URL, password)

Create log parsing regex for extracting timestamps, IPs, and error codes

Design search-and-replace rules for text processing pipelines

Validate data extraction patterns before deploying to production

Debug why a regex pattern is not matching expected input

About Regex Tester

Regular expressions are powerful but error-prone — a small mistake can cause unexpected matches, missed captures, or catastrophic backtracking. This regex tester helps you catch issues before they reach production. It uses JavaScript's native RegExp engine, so patterns behave exactly as they would in your JavaScript/TypeScript code. The tool highlights all matches in the test string, shows capture group contents, and displays match positions. For complex patterns, use the flag toggles to test behavior with different modes. Common regex patterns: email validation (^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$), URL matching, phone numbers, IP addresses, and date formats.

Frequently Asked Questions

What regex syntax does this tester support?: It uses JavaScript's native RegExp engine, supporting all standard regex syntax including character classes, quantifiers, lookaheads, lookbehinds (ES2018+), named capture groups, and Unicode property escapes.
What regex flags are available?: All JavaScript regex flags: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — . matches newlines), u (unicode), and y (sticky).
How do I test capture groups?: Add parentheses in your pattern to create capture groups. The tool displays all captured values with their group numbers. For named groups, use (?<name>pattern) syntax and the tool shows the group names.
Can I test regex replacement patterns?: Yes. Enter a replacement string using $1, $2 backreferences for captured groups, or $& for the full match. The tool shows the replacement result in real time.
Can I use this as a Ruby regex test tool?: Yes. Most standard regex patterns work the same in Ruby and JavaScript — character classes, quantifiers, anchors, and groups are cross-compatible. This regex check online tool is ideal for testing Ruby regex patterns. Note that Ruby-specific features like \p{Hiragana} or (?<name>) named groups have slightly different syntax.
Will my regex work the same in Python or Java?: Regex syntax varies between languages. This tester uses JavaScript regex. Most basic patterns work cross-language, but features like lookbehinds, named groups, and flags may differ in Python, Java, Ruby, or Go.
Is this regex tester free?: Yes. Completely free, runs locally in your browser, and has no limits on pattern testing or registration requirements.

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Use Cases

Build and test form validation patterns (email, phone, URL, password)

Create log parsing regex for extracting timestamps, IPs, and error codes

Design search-and-replace rules for text processing pipelines

Validate data extraction patterns before deploying to production

Debug why a regex pattern is not matching expected input

Frequently Asked Questions

What regex syntax does this tester support?

It uses JavaScript's native RegExp engine, supporting all standard regex syntax including character classes, quantifiers, lookaheads, lookbehinds (ES2018+), named capture groups, and Unicode property escapes.

What regex flags are available?

All JavaScript regex flags: g (global — find all matches), i (case-insensitive), m (multiline — ^ and $ match line boundaries), s (dotAll — . matches newlines), u (unicode), and y (sticky).

How do I test capture groups?

Add parentheses in your pattern to create capture groups. The tool displays all captured values with their group numbers. For named groups, use (?<name>pattern) syntax and the tool shows the group names.

Can I test regex replacement patterns?

Yes. Enter a replacement string using $1, $2 backreferences for captured groups, or $& for the full match. The tool shows the replacement result in real time.

Can I use this as a Ruby regex test tool?

Yes. Most standard regex patterns work the same in Ruby and JavaScript — character classes, quantifiers, anchors, and groups are cross-compatible. This regex check online tool is ideal for testing Ruby regex patterns. Note that Ruby-specific features like \p{Hiragana} or (?<name>) named groups have slightly different syntax.

Will my regex work the same in Python or Java?

Regex syntax varies between languages. This tester uses JavaScript regex. Most basic patterns work cross-language, but features like lookbehinds, named groups, and flags may differ in Python, Java, Ruby, or Go.

Is this regex tester free?

Yes. Completely free, runs locally in your browser, and has no limits on pattern testing or registration requirements.

Regex Check Online — Regular Expression Tester & Debugger

Key Takeaways

What is Regex Tester?

How to Use Regex Tester

Key Features

Use Cases

About Regex Tester

Frequently Asked Questions

Regex Check Online — Regular Expression Tester & Debugger

Quick Pattern Templates

Key Takeaways

What is Regex Tester?

How to Use Regex Tester

Key Features

Use Cases

About Regex Tester

Frequently Asked Questions

Quick Pattern Templates

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Regex Check Online — Regular Expression Tester & Debugger

Key Takeaways

What is Regex Tester?

How to Use Regex Tester

Key Features

Use Cases

About Regex Tester

Frequently Asked Questions

Regex Check Online — Regular Expression Tester & Debugger

Quick Pattern Templates

Key Takeaways

What is Regex Tester?

How to Use Regex Tester

Key Features

Use Cases

About Regex Tester

Frequently Asked Questions

Quick Pattern Templates