Free Regex Tester

Test and debug your regular expressions instantly with our powerful regex tester. Get real-time pattern matching, capture groups analysis, and detailed explanations to perfect your regex patterns.

Test Your Regex Pattern

Enter your regular expression pattern and test text to see matches in real-time

Quick Start Examples

Click any example to load it into the tester

Match Results

Enter a regex pattern and test text to see results

Complete Regex Tester Guide: Master Regular Expressions Online

Learn how to test, debug, and optimize regular expression patterns with our comprehensive regex validator guide. Perfect for beginners and advanced developers.

How to Use This Online Regex Pattern Tester

Our regular expression testing tool provides instant feedback for pattern matching, making it easy to validate email addresses, phone numbers, URLs, and custom data formats. Simply follow these four steps to start testing regex patterns online:

Step 1: Enter Your Regex Pattern

Type your regular expression in the pattern field. Don't include delimiters like forward slashes unless they're part of your pattern. For example, to match email addresses, use: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]2

💡 Try our pre-built examples below to see patterns in action!

Step 2: Add Test Text

Enter the text you want to test your pattern against. You can paste multiple lines, log files, CSV data, or large blocks of text. Our regex matcher processes up to 1MB of text instantly.

💡 Use our word counter to analyze text length first.

Step 3: Configure Flags

Choose flags like case insensitive (i), multiline (m), or dot-all (s) to modify pattern behavior. These flags match the standard PCRE syntax used in JavaScript, Python, PHP, and Java.

💡 Flags are essential for matching across line breaks!

Step 4: View Real-Time Results

See instant matches, capture groups, execution time (in microseconds), and pattern complexity analysis. Our regex debugger shows exactly what matched, where it matched, and warns about performance issues.

💡 Green = success, Red = error, Yellow = warning

Regular Expression Basics: Character Classes and Metacharacters

Understanding regex character classes is fundamental to writing effective patterns. These special sequences match specific types of characters in your text:

Character Classes for Pattern Matching

. Matches any character except newline (use \s flag to include)

\d Matches any digit (0-9), equivalent to [0-9]

\w Matches word characters (a-z, A-Z, 0-9, _) used for variable names

\s Matches whitespace (space, tab, newline, carriage return)

[a-z] Matches any lowercase letter from a to z

[0-9] Matches any single digit, same as \d

[^a-z] Negated class: matches anything NOT a lowercase letter

\D Matches non-digits, opposite of \d

💡 Pro tip: Use character classes for form validation in React, Vue, and Angular applications. Learn more at MDN Web Docs.

Regex Quantifiers for Repetition Matching

Quantifiers specify how many times a character or group should match. Essential for validating phone numbers, zip codes, and password requirements:

* Zero or more - Example: colou*r matches "color" or "colour"

+ One or more - Example: \d+ matches "123" but not empty string

? Zero or one (optional) - Example: https? matches "http" or "https"

{"n"} Exactly n - Example: \d{3} matches exactly 3 digits like "123"

{"n,m"} Between n and m - Example: \d{3,5} matches 3 to 5 digits

{"n,"} n or more - Example: \w{8,} matches 8+ word characters

🔍 Real-world use: \d{3}-\d{2}-\d{4} matches SSN format "123-45-6789". Use our random string generator to create test data.

Regex Anchors and Word Boundaries

Anchors and assertions let you match positions rather than characters. Critical for exact string validation:

^ Start of string/line - ^Hello only matches if "Hello" starts the line

$ End of string/line - world$ only matches if "world" ends the line

\b Word boundary - \bcat\b matches "cat" but not "scatter"

\B Non-word boundary - \Bcat matches "scatter" but not "cat"

⚡ Pro tip: Use ^...$ for exact full-string validation (username, email). Remove anchors for substring matching in log files.

Common Regex Patterns for Web Development

These production-ready regex patterns are used by developers worldwide for email validation, phone number formatting, and data extraction. Copy and test them in our regex tester above:

📧 Email Address Validation Regex

[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]2

Matches standard email addresses like user@example.com, john.doe@company.co.uk

⚠️ For RFC 5322 compliant validation, use more comprehensive patterns.

US Phone Number

$\d3$\s\d3-\d4

Matches phone numbers in format (555) 123-4567

URL

https?://[^\s]+

Matches HTTP and HTTPS URLs

IPv4 Address

((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.)3(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)

Matches valid IPv4 addresses like 192.168.1.1

Date (ISO Format)

\d4-\d2-\d2

Matches dates in YYYY-MM-DD format

Hex Color Code

#([A-Fa-f0-9]6|[A-Fa-f0-9]3)

Matches hex colors like #FF0000 or #F00

Understanding Flags

Case Insensitive (i)

Makes the pattern match regardless of letter case.

Pattern: hello

Text: Hello WORLD hello

Without flag: 1 match | With flag: 2 matches

Multiline (m)

Makes ^ and $ match start/end of each line, not just the entire string.

Pattern: ^word

Text: first line\nword at start\nlast line

Without flag: 0 matches | With flag: 1 match

Dot All (s)

Makes the . character match newline characters as well.

Pattern: start.*end

Text: start\nmiddle\nend

Without flag: 0 matches | With flag: 1 match

Best Practices

Do's

Test your patterns with various input examples

Use word boundaries (\b) instead of anchors for partial matches

Escape special characters when matching literally

Use non-capturing groups (?:) when you don't need the group

Keep patterns simple and readable

Don'ts

Avoid nested quantifiers like (.+)+ that cause backtracking

Don't use regex for parsing complex nested structures

Don't make patterns overly complex for simple tasks

Don't ignore case sensitivity requirements

Don't forget to test edge cases and empty inputs

Troubleshooting Common Issues

Pattern doesn't match anything

• Check if you're using anchors (^ $) when you want partial matches
• Verify your character classes and ranges are correct
• Make sure special characters are properly escaped
• Test with simpler versions of your pattern first

Pattern matches too much

• Add word boundaries (\b) to prevent partial word matches
• Use more specific character classes instead of . (dot)
• Consider using non-greedy quantifiers (*? +? ??)
• Add anchors if you need exact full-string matches

Performance warnings

• Avoid nested quantifiers like (.*)+ or (.+)+
• Use atomic groups or possessive quantifiers when possible
• Keep alternation (|) options specific and ordered by likelihood
• Consider breaking complex patterns into multiple simpler ones

Related Developer Tools

String Case Converter

Convert text between camelCase, snake_case, kebab-case, and more. Perfect for testing regex case sensitivity.

Word Counter Tool

Count characters, words, and lines in your test data. Analyze text before regex matching.

Random String Generator

Generate test strings, passwords, and sample data to test your regex patterns thoroughly.

📚 Learn More About Regular Expressions:

Regular-Expressions.info MDN Regex Guide RegExr Community PCRE Documentation

Free Online Regex Tester and Debugger for Developers

Test, debug, and optimize regular expression patterns instantly with real-time matching, performance analysis, and syntax validation. Our regex validator helps you write better patterns for JavaScript, Python, PHP, Java, and Go applications.

Why Developers Choose Our Online Regex Tester

Lightning-Fast Real-Time Regex Testing

See matches, capture groups, and pattern behavior as you type. No server roundtrips, no delays - just instant client-side validation for patterns up to 10,000 characters. Perfect for validating email formats, phone numbers, and complex log parsing patterns.

Intelligent Pattern Analysis and Optimization

Get automatic detection of catastrophic backtracking, complexity scoring (low/medium/high), execution time in microseconds, and specific optimization suggestions. Our regex debugger identifies nested quantifiers, greedy patterns, and inefficient alternations that could cause performance issues in production.

100% Private Client-Side Processing

Your regex patterns and sensitive test data never leave your browser - all matching, analysis, and validation happens locally using JavaScript. No server uploads, no data logging, no tracking. Completely GDPR compliant for testing proprietary code patterns and confidential data formats.

Real-World Regex Use Cases Developers Face Daily

✅ Email Validation - RFC 5322 compliant patterns

✅ Form Input Sanitization - React/Vue/Angular validators

✅ Apache/Nginx Log Parsing - Extract IPs, status codes

✅ CSV/JSON Data Extraction - Parse structured text

✅ URL Route Matching - Express, Django, Rails patterns

✅ Credit Card Masking - PCI compliance patterns

✅ Markdown Parsing - Extract headers, links, code

✅ SQL Injection Prevention - Input sanitization

✅ API Response Validation - JSON schema patterns

✅ Password Strength Rules - Enforce complexity

✅ Config File Parsing - YAML, INI, ENV variables

✅ Phone Number Formatting - International E.164

💡 Need to process text after matching? Try our word counter and string case converter tools.

Common Regex Patterns Developers Need

Email Validation Regex

[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}

Validates standard email addresses with proper domain structure and TLD requirements.

Phone Number Regex

$\d{3}$\s\d{3}-\d{4}

Matches US phone numbers in (555) 123-4567 format with proper spacing and formatting.

URL Validation Regex

https?://[^\s]+

Captures HTTP and HTTPS URLs from text, perfect for link extraction and validation.

IP Address Regex

((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)

Validates IPv4 addresses with proper range checking for each octet (0-255).

Password Strength Regex

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}

Enforces strong passwords with uppercase, lowercase, numbers, and special characters.

Date Format Regex

\d{4}-\d{2}-\d{2}

Matches ISO date format (YYYY-MM-DD) commonly used in databases and APIs.

Regular Expression Use Cases

Form Validation

Validate user input in real-time with custom regex patterns for emails, phones, and custom formats.

Data Extraction

Extract specific data patterns from logs, CSV files, and unstructured text efficiently.

Code Analysis

Parse source code, find patterns, and automate refactoring tasks with precise regex matching.

Log Processing

Parse server logs, extract error patterns, and monitor system health with regex-based filtering.

Start Testing Your Regex Patterns Now

Join thousands of developers who trust our regex tester for accurate pattern validation, debugging, and optimization. No signup required - start testing immediately.

100% Free Tool No Registration Real-Time Results Privacy Focused Expert Analysis

Regex Tester FAQ: Common Questions About Regular Expression Testing

🔍 What makes this online regex tester better than other regex validators?

Unlike basic regex testers, we provide comprehensive pattern analysis including: (1) Real-time execution time measurement in microseconds, (2) Automatic catastrophic backtracking detection, (3) Pattern complexity scoring (low/medium/high), (4) Detailed capture group extraction with position indices, and (5) Performance optimization suggestions.

We also show exactly which regex features your pattern uses (lookaheads, backreferences, character classes) to help you understand what your pattern actually does.

🚩 Can I test multiline regex patterns with different flags?

Yes! Our regex debugger supports all standard regex flags: case insensitive (i) for matching "Hello" and "hello", multiline (m) for making ^ and $ match line boundaries, and dot-all (s) for making . match newlines. You can enable multiple flags simultaneously and see instant results.

Example: The pattern start.*end with dot-all flag enabled will match text spanning multiple lines like "start\nmiddle\nend".

🔒 Is my regex pattern and test data secure? Does it get stored?

Absolutely secure. Our regex tester runs 100% client-side in your browser using JavaScript - zero data is transmitted to our servers. Your sensitive patterns (API keys, database schemas, proprietary formats) and test data never leave your device. No cookies, no analytics tracking, no server logs.

This makes our tool completely GDPR compliant and safe for testing confidential data patterns in enterprise environments.

⚡ How do I avoid catastrophic backtracking in my regular expressions?

Our tool automatically detects dangerous patterns that can cause catastrophic backtracking (exponential time complexity). Common culprits include: nested quantifiers like (a+)+, overlapping alternations like (a|a)*, and unanchored greedy patterns.

When we detect these issues, we show a yellow warning with specific suggestions like: "Use atomic groups", "Make quantifier possessive", or "Add anchors to limit backtracking".

💻 Which programming languages are compatible with this regex tester?

Our regex engine uses PCRE (Perl Compatible Regular Expressions) syntax, which is the most widely adopted regex flavor. This means patterns tested here will work in: JavaScript (Node.js, React, Vue), Python (re module), PHP (preg functions), Java (Pattern class), C# (.NET Regex), Go (regexp package), Ruby, and Perl.

⚠️ Note: Some advanced features like lookbehinds or Unicode properties may have limited support in older JavaScript engines. Check MDN compatibility tables for browser-specific details.

📝 Can I save my regex patterns for later use?

Currently, patterns are stored temporarily in your browser's session. We recommend copying your tested patterns to a password-protected note or version control system like GitHub. For team collaboration, consider creating a shared regex pattern library in your project documentation.

💡 Pro tip: Use descriptive comments in your code when implementing regex patterns, like: // Validates ISO 8601 dates: YYYY-MM-DD