Online Regex Tester & Debugger
Test regular expressions with real-time highlighting and instant results
📖 How to Use
- Enter your regular expression pattern in the first field using the format
/pattern/flags - Add test strings in the second field, one per line
- See matching results highlighted in green in real-time
- Non-matching lines appear in gray for easy comparison
- Copy your regex pattern using the copy button
- The match count shows how many lines matched your pattern
About the Online Regex Tester
The Online Regex Tester is a free browser-based utility that allows developers to test and validate regular expression patterns in real-time. Whether you're validating email addresses, parsing log files, or extracting data from text, this tool helps you perfect your regex patterns before deploying to production. With instant visual feedback and support for all JavaScript regex flags, you can quickly identify issues and optimize your patterns for maximum efficiency.
Key Features:
- Real-time pattern matching with instant visual feedback
- 100% client-side processing - your data never leaves your browser
- No registration, login, or installation required
- Supports all JavaScript regex syntax and flags (g, i, m, u, y, s)
- Mobile-friendly responsive interface
- Copy-to-clipboard functionality for easy pattern transfer
Common Use Cases:
- Email Validation: Test email regex patterns to ensure they catch valid addresses while rejecting invalid ones
- Data Extraction: Extract specific patterns from log files, CSV data, or API responses
- Form Validation: Validate user input for phone numbers, postal codes, credit cards, and custom formats
- Text Processing: Find and replace patterns in large text files or clean up data before importing
- URL Parsing: Extract domains, paths, query parameters, or validate URL formats
Common Regex Patterns & Examples
Email Validation
/^[^\s@]+@[^\s@]+\.[^\s@]+$/Matches: [email protected], [email protected], [email protected]
Does not match: invalid@, @domain.com, user@domain, missing-tld@domain
URL Validation
/^https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b/Matches: https://example.com, http://www.test.com/path, https://sub.domain.co
Use case: Validate user-submitted URLs in forms or extract links from text
Phone Number (US Format)
/^(\+1)?[-.\s]?\(?[0-9]3\)?[-.\s]?[0-9]3[-.\s]?[0-9]4$/Matches: (555) 123-4567, 555-123-4567, +1 555 123 4567, 5551234567
Use case: Validate and format phone numbers in contact forms
Alphanumeric with Underscores (Username)
/^[a-zA-Z0-9_]{3,16}$/Matches: user_123, JohnDoe, test_user_2024
Use case: Validate usernames (3-16 characters, alphanumeric and underscores only)
Hex Color Code
/^#([A-Fa-f0-9]6|[A-Fa-f0-9]3)$/Matches: #FF5733, #f90, #1a2b3c, #ABC
Use case: Validate hex color codes in CSS or design tools
IPv4 Address
/^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.)3(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/Matches: 192.168.1.1, 10.0.0.255, 172.16.0.1
Use case: Validate IP addresses in network configuration forms
❓ Frequently Asked Questions
What is a regex tester and why do I need one?
A regex tester is an online tool that allows you to test regular expression patterns against sample text in real-time. It's essential for developers because it helps validate regex patterns before implementing them in code, saving debugging time and preventing production errors. Our regex tester provides instant feedback with syntax highlighting and match visualization.
How do I test regex online with your tool?
Simply enter your regex pattern in the first field (including delimiters and flags, e.g., /pattern/gi), then paste your test strings in the second field (one per line). The tool automatically highlights matches in real-time as you type. You can copy results using the copy button or adjust your pattern to refine matches.
What regex syntax and flags are supported?
Our regex tester supports full JavaScript regex syntax including all standard patterns, character classes, quantifiers, and special characters. Supported flags include: g (global), i (case-insensitive), m (multiline), u (unicode), y (sticky), and s (dotAll). The tool uses the same regex engine as modern browsers.
Is my data secure when using this regex tester?
Yes, absolutely. All regex testing happens entirely in your browser using client-side JavaScript. Your regex patterns and test strings never leave your device or get sent to any server. We don't log, store, or track any of your data. This makes it safe to test even sensitive or confidential text patterns.
Can I save my regex patterns for later use?
Currently, the tool doesn't include built-in pattern saving. However, you can bookmark the page or save your regex patterns in your code editor or a note-taking app. We recommend copying your tested patterns immediately after validation.
What's the difference between regex tester tools?
Different regex testers support different regex engines (JavaScript, PCRE, Python, etc.). Our tool uses JavaScript regex engine, which is ideal for web development. Other differences include features like pattern libraries, code generation, debugging tools, and performance. Our tool focuses on speed, privacy, and simplicity.
How do I match email addresses with regex?
A simple email regex pattern is: /^[^\s@]+@[^\s@]+\.[^\s@]+$/. This matches most common email formats. For more comprehensive validation (supporting all RFC standards), you'll need a more complex pattern. We recommend using this simple pattern for basic validation and server-side verification for production systems.
Can I test regex for multiple programming languages?
Our tool uses JavaScript regex syntax, which is similar to many other languages but has some differences. For language-specific testing (Python, PHP, Java, .NET), you may need specialized tools. However, most basic patterns work across languages, making our tool useful for learning and quick testing.