Regex Tester

What is a Regex Tester?

A regex tester is a tool that helps developers test, validate, and debug regular expressions (regex patterns). Regular expressions are powerful pattern-matching strings used to search, extract, and validate text data. Testing regex patterns is essential for ensuring they work correctly before using them in code.

Why Use a Regex Tester?

Regular expressions can be complex and difficult to debug. A regex tester helps you:

• Test Patterns: Verify regex patterns work as expected before implementing in code
• Debug Issues: Identify why a pattern isn't matching or matching incorrectly
• Learn Regex: Understand how regex patterns work through visual feedback
• Validate Input: Test patterns for form validation, data extraction, or text processing
• Save Time: Catch regex errors early instead of debugging in production code

Common Use Cases

Form Validation

Test regex patterns for validating email addresses, phone numbers, URLs, passwords, and other form inputs. Ensure your validation patterns work correctly before deploying.

Data Extraction

Test patterns for extracting specific data from text, logs, or documents. Verify capture groups work correctly to extract the right information.

Text Processing

Test regex patterns for search and replace operations, text parsing, or data cleaning. Ensure patterns match the intended text segments.

API Development

Validate regex patterns used in API route definitions, query parameter validation, or request body validation.

Log Analysis

Test patterns for parsing log files, extracting timestamps, error messages, or specific log entries.

Regex Flags Explained

JavaScript regex flags modify pattern matching behavior:

• g (global): Find all matches, not just the first
• i (case-insensitive): Match regardless of case
• m (multiline): ^ and $ match line boundaries, not just string boundaries
• y (sticky): Match only at the lastIndex position
• u (unicode): Enable full Unicode matching

Common Regex Patterns

Email Validation

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

Phone Number

^\+?[1-9]\d{1,14}$ (international format)

URL Matching

https?://[\w\-]+(\.[\w\-]+)+([\w\-.,@?^=%&:/~+#]*[\w\-@?^=%&/~+#])?

Date Format (YYYY-MM-DD)

^\d{4}-\d{2}-\d{2}$

Password Strength

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

Regex Testing Best Practices

• Test Edge Cases: Test with empty strings, special characters, and boundary conditions
• Use Sample Data: Test with realistic data that matches your use case
• Check All Flags: Verify behavior with different flag combinations
• Validate Groups: Ensure capture groups extract the correct data
• Performance: Be aware that complex patterns can be slow on large text

Common Regex Mistakes

• Greedy vs Lazy: Use ? for lazy matching when needed (.*? vs .*)
• Escaping: Remember to escape special characters (\. for literal dot)
• Anchors: Use ^ and $ to match entire strings, not substrings
• Character Classes: Use [0-9] instead of \d when you need explicit ranges
• Quantifiers: Be specific with quantifiers ({3,5} vs + or *)

Privacy and Security

Our Regex Tester processes all data entirely in your browser. No text or patterns are sent to our servers, ensuring complete privacy for sensitive data.

Related Tools

If you need other developer tools, check out:

• JSON Formatter: Format and validate JSON data
• Base64 Encode/Decode: Encode and decode Base64 data
• JWT Parser: Decode and analyze JWT tokens