Utilities

Regex Tester

Test and debug regular expressions with real-time matching, capture groups, and extended flags

Regex Pattern

Escape

Test String

[email protected] [email protected]

2 matches found

#1idx:0len:16

[email protected]

Capture Groups:

$1:user

$2:example

$3:com

#2idx:17len:14

[email protected]

Capture Groups:

$1:admin

$2:test

$3:org

All processing is done client-side. Your data never leaves your browser.

About

Real-time regex tester supporting flags (g/i/m/s/u/y), capture groups, named groups, and non-capturing groups with match highlighting. Includes a common patterns library, replace/split modes, an auto-escape feature, and a built-in cheat sheet.

Writing and debugging regular expressions is error-prone without instant feedback; this tool eliminates guesswork by showing matches live as you type. It also educates users through the cheat sheet and common patterns library.

Who should use this tool?

Developers, data analysts, and anyone who needs to build, test, or debug regular expressions across any programming language.

Common use cases

Debug a complex regex with nested capture groups and lookaheads
Learn regex syntax using the built-in cheat sheet and common patterns library
Test a replacement pattern in replace mode before using it in production code
Split a CSV line using split mode with a delimiter regex
Validate email/URL/phone patterns from the common patterns library
Quickly escape special regex characters in a literal string using auto-escape

How to Use

Type or paste a regex pattern into the pattern input field; flags (g, i, m, s, u, y) can be toggled via checkboxes below it.

Enter test text in the input area; all matches are highlighted in real time with colors distinguishing capture groups.

Click a pattern from the Common Patterns library (email, URL, date, IP, etc.) to load it instantly.

Switch between Match, Replace, and Split modes using the tab bar above the output panel.

Refer to the cheat sheet by clicking the help icon; it covers anchors, quantifiers, character classes, and flags.

Use the auto-escape button to escape all special regex characters in a selected or pasted literal string.

Examples

Input: pattern /\b(\w+)\s\1\b/gi with text "hello hello world" → matches "hello hello" showing repeated word capture group

Input: pattern /(\d{4})-(\d{2})-(\d{2})/ in replace mode with replacement "$3/$2/$1" on "2025-12-25" → output "25/12/2025"

Best Practices

Always anchor patterns (^ and $) when matching entire strings to avoid partial matches
Prefer non-capturing groups (?:...) when you do not need to capture to improve performance
Test edge cases like empty strings, very long inputs, and special Unicode characters
Use the auto-escape feature when treating user input as literal text in a regex
Start simple and add complexity incrementally, verifying each step with the live preview

Common Mistakes

Forgetting to escape special characters like . + * ? [ ] ( ) { } ^ $ | \\
Overusing .* which can lead to catastrophic backtracking on large inputs
Assuming regex is the same across all engines (PCRE, JS, Python, etc.) — flags and features vary
Using greedy quantifiers when lazy ones (*? +?) would be more appropriate
Neglecting the m flag when using ^ and $ with multi-line strings

FAQ

What is the difference between greedy and lazy quantifiers? Greedy (*, +) matches as much as possible; lazy (*?, +?) matches as little as possible while still satisfying the pattern.

Why does my regex match more than expected? You likely have an unanchored pattern or used a greedy quantifier

try adding ^/$ or switching to lazy.

What does the s flag do? The s flag (dotAll) makes . match newline characters; without it, . matches everything except newlines.

Can I use named groups? Yes

use the syntax (?<name>...) for named capture groups. They appear in the match details panel.

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Learning Resources

Dive deeper with our comprehensive guides and tutorials.

Regex Tester - Beginner's Guide

5 min read

Regex Tester Advanced Techniques

8 min read

Regex Tester

Test and debug regular expressions with real-time matching, capture groups, and extended flags

Regex Pattern

Escape

Test String

[email protected] [email protected]

2 matches found

#1idx:0len:16

[email protected]

Capture Groups:

$1:user

$2:example

$3:com

#2idx:17len:14

[email protected]

Capture Groups:

$1:admin

$2:test

$3:org

All processing is done client-side. Your data never leaves your browser.

About

Who should use this tool?

Developers, data analysts, and anyone who needs to build, test, or debug regular expressions across any programming language.

Common use cases

Debug a complex regex with nested capture groups and lookaheads
Learn regex syntax using the built-in cheat sheet and common patterns library
Test a replacement pattern in replace mode before using it in production code
Split a CSV line using split mode with a delimiter regex
Validate email/URL/phone patterns from the common patterns library
Quickly escape special regex characters in a literal string using auto-escape

How to Use

Type or paste a regex pattern into the pattern input field; flags (g, i, m, s, u, y) can be toggled via checkboxes below it.

Enter test text in the input area; all matches are highlighted in real time with colors distinguishing capture groups.

Click a pattern from the Common Patterns library (email, URL, date, IP, etc.) to load it instantly.

Switch between Match, Replace, and Split modes using the tab bar above the output panel.

Refer to the cheat sheet by clicking the help icon; it covers anchors, quantifiers, character classes, and flags.

Use the auto-escape button to escape all special regex characters in a selected or pasted literal string.

Best Practices

Always anchor patterns (^ and $) when matching entire strings to avoid partial matches

Prefer non-capturing groups (?:...) when you do not need to capture to improve performance

Test edge cases like empty strings, very long inputs, and special Unicode characters

Use the auto-escape feature when treating user input as literal text in a regex

Start simple and add complexity incrementally, verifying each step with the live preview

Common Mistakes

Forgetting to escape special characters like . + * ? [ ] ( ) { } ^ $ | \\

Overusing .* which can lead to catastrophic backtracking on large inputs

Assuming regex is the same across all engines (PCRE, JS, Python, etc.) — flags and features vary

Using greedy quantifiers when lazy ones (*? +?) would be more appropriate

Neglecting the m flag when using ^ and $ with multi-line strings

FAQ

What is the difference between greedy and lazy quantifiers? Greedy (*, +) matches as much as possible; lazy (*?, +?) matches as little as possible while still satisfying the pattern.

Why does my regex match more than expected? You likely have an unanchored pattern or used a greedy quantifier

try adding ^/$ or switching to lazy.

What does the s flag do? The s flag (dotAll) makes . match newline characters; without it, . matches everything except newlines.

Can I use named groups? Yes

use the syntax (?<name>...) for named capture groups. They appear in the match details panel.

Regex Tester

About

Who should use this tool?

Common use cases

How to Use

Examples

Best Practices

Common Mistakes

FAQ

Related Tools

Same Category — Utilities

Word Counter

Markdown Preview

IP Address Calculator

JSON Path Finder

Popular Tools

JSON Formatter

Base64 Encoder/Decoder

JWT Decoder

Learning Resources

Share

Regex Tester

About

Who should use this tool?

Common use cases

How to Use

Examples

Best Practices

Common Mistakes

FAQ

Related Tools

Same Category — Utilities

Word Counter

Markdown Preview

IP Address Calculator

JSON Path Finder

Popular Tools

JSON Formatter

Base64 Encoder/Decoder

JWT Decoder

Learning Resources

Share