Test and validate regular expressions
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Our free online Regex Tester (Regular Expression Tester) is a powerful tool for testing, validating, and debugging regular expressions. Whether you're a developer, data analyst, or system administrator, this tool helps you create and test regex patterns with instant feedback. Test your regular expressions against sample text, see matches in real-time, and refine your patterns until they work perfectly.
Using our regex tester is straightforward and intuitive. Enter your regular expression pattern in the "Regular Expression" field. Add any flags you need (g for global, i for case-insensitive, m for multiline) in the "Flags" field. Type or paste your test string in the "Test String" textarea. Click "Test Regex" to see all matches highlighted. The tool displays the number of matches found and shows each match in a separate highlighted box. If there's an error in your regex syntax, you'll see a clear error message to help you debug.
Regular expressions (regex or regexp) are powerful patterns used for matching text. They provide a concise and flexible means for identifying strings of text, such as particular characters, words, or patterns of characters. Regular expressions are used in programming languages, text editors, command-line tools, and many applications for search and replace operations, input validation, data extraction, and text parsing. A regex pattern consists of ordinary characters (like letters and digits) and special metacharacters (like ., *, +, ?, [], , ^, $) that define the search pattern.
Email Validation: ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ - Matches standard email addresses for form validation and user input verification.
Phone Numbers: \d{3}-\d{3}-\d{4} - Matches phone numbers in XXX-XXX-XXXX format for contact information validation.
URLs: https?://[a-zA-Z0-9.-]+\.[a-zA-Z]{2,} - Matches HTTP and HTTPS URLs for link extraction and validation.
Dates: \d{2}/\d{2}/\d{4} - Matches dates in MM/DD/YYYY format for date parsing and validation.
IP Addresses: \d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3} - Matches IPv4 addresses for network configuration and log parsing.
Credit Cards: \d{4}[- ]?\d{4}[- ]?\d{4}[- ]?\d{4} - Matches credit card numbers for payment form validation.
g (global): Finds all matches in the string instead of stopping after the first match. Essential for finding multiple occurrences of a pattern.
i (case-insensitive): Makes the pattern match regardless of letter case. 'A' and 'a' are treated as the same character.
m (multiline): Changes ^ and $ to match the start/end of each line rather than the entire string. Useful for processing multi-line text files.
s (dotAll): Makes the dot (.) match newline characters as well. Without this flag, dot matches everything except newlines.
u (unicode): Enables full Unicode support for the pattern. Necessary when working with Unicode characters and emoji.
Form Validation: Test regex patterns for validating user input in web forms, including emails, phone numbers, passwords, usernames, and postal codes. Ensure patterns work correctly before deploying to production.
Data Extraction: Develop patterns to extract specific information from logs, HTML, CSV files, or unstructured text. Test patterns against sample data to verify they capture the correct information.
Text Processing: Create patterns for find-and-replace operations in large documents, code refactoring, or text transformation tasks. Test to ensure you don't match unintended strings.
Log Analysis: Build regex patterns to parse and analyze log files from web servers, applications, or systems. Extract timestamps, error codes, IP addresses, or specific events.
Security: Develop patterns to detect malicious input, SQL injection attempts, XSS attacks, or suspicious patterns in user-submitted data.
Search and Replace: Test complex search patterns before performing bulk find-and-replace operations in code editors, databases, or document processors.
Character Classes: [abc] matches any single character a, b, or c. [^abc] matches any character except a, b, or c. [a-z] matches any lowercase letter.
Quantifiers: * (0 or more), + (1 or more), ? (0 or 1), {n} (exactly n), {n,} (n or more),{n,m} (between n and m times).
Anchors: ^ matches the start of a string, $ matches the end. \b matches word boundaries, useful for finding whole words.
Shortcuts: \d (digits), \w (word characters), \s (whitespace), \D (non-digits), \W (non-word characters), \S (non-whitespace).
Groups: ( ) creates capturing groups for extracting matched portions. (?: ) creates non-capturing groups for grouping without capturing.
Start Simple: Begin with basic patterns and gradually add complexity. Test at each step to ensure the pattern works as expected.
Be Specific: Avoid overly greedy patterns that match more than intended. Use specific character classes and quantifiers to match exactly what you need.
Test Thoroughly: Test your regex against various inputs including edge cases, empty strings, special characters, and unexpected formats.
Use Comments: For complex patterns, use the x flag (in languages that support it) to add whitespace and comments for readability.
Optimize Performance: Avoid catastrophic backtracking by being careful with nested quantifiers. Test performance with large inputs.
Consider Alternatives: Sometimes simple string methods or parsing libraries are more appropriate than complex regex patterns.
When your regex doesn't work as expected, use our tester to debug step by step. Break down complex patterns into smaller parts and test each component. Check for unescaped special characters, incorrect quantifiers, or missing anchors. Verify that your flags are set correctly. Test with multiple sample inputs to identify edge cases where the pattern fails. Common mistakes include forgetting to escape special characters, using greedy quantifiers when lazy ones are needed, and incorrect group capturing. Our regex tester provides immediate feedback, making debugging faster and more efficient.
Your privacy is guaranteed with our regex tester. All pattern testing and matching happens entirely in your browser using JavaScript. We don't send your regular expressions, test strings, or any data to our servers. Your sensitive patterns, test data, and validation rules remain completely private on your device. The tool works offline once loaded, providing maximum security for testing confidential data patterns, proprietary validation rules, and sensitive text processing. You can safely test regex patterns for security applications, personal data validation, and confidential text processing without any privacy concerns.