Regex Tester

Test and debug regular expressions with real-time matching. Validate regex patterns with highlighting and explanations.

What It Does

A Regex Tester (Regular Expression Tester) is an interactive tool that helps developers and data professionals test, debug, and validate regular expression patterns in real-time. Regular expressions (regex) are powerful pattern-matching sequences used to search, match, and manipulate text. This tool provides instant visual feedback, highlighting matches in your test text and helping you understand how your regex pattern behaves before implementing it in your code.

Key Features:

  • Real-time pattern matching with instant visual feedback and highlighting
  • Support for common regex flags (global, case-insensitive, multiline, dotall, unicode)
  • Match highlighting with numbered capture groups and backreferences
  • Detailed match information including position, length, and captured groups
  • Common regex pattern library with frequently used expressions
  • Syntax error detection with helpful error messages
  • Support for multiple regex flavors and standards

How To Use

Testing regular expressions is straightforward with our regex tester. Follow these steps to validate your patterns and ensure they match your target text correctly.

1

Enter Your Regular Expression

Type or paste your regex pattern into the pattern input field. You can include special characters like \d (digits), \w (word characters), \s (whitespace), quantifiers (* + ? {}), anchors (^ $), and character classes ([abc]).

2

Add Test Text

Enter the text you want to test against your pattern in the test string area. This can be a single line or multiple lines of text depending on your needs.

3

Select Regex Flags

Choose appropriate flags: g (global - find all matches), i (case-insensitive), m (multiline - ^ and $ match line breaks), s (dotall - . matches newlines), or u (unicode).

4

Review Match Results

Instantly see all matches highlighted in your test text. View detailed information about each match including position, matched text, and any captured groups.

5

Refine Your Pattern

Adjust your regex pattern based on the results. The tool updates matches in real-time, making it easy to iterate and perfect your expression.

Pro Tips

  • •Start with simple patterns and gradually add complexity
  • •Use capture groups ( ) to extract specific parts of matches
  • •Test with multiple varied examples to ensure your pattern works in all cases
  • •Remember that backslashes need to be escaped in most programming languages
  • •Use anchors (^ $) to match the start or end of strings
  • •Leverage character classes like \d for digits, \w for word characters

Benefits

Save development time by testing patterns before implementation
Avoid runtime errors and unexpected behavior in production code
Learn regex syntax through experimentation and instant feedback
Debug complex patterns with visual match highlighting
Validate data formats like emails, phone numbers, and URLs
Improve code quality with thoroughly tested regex patterns
Share patterns with team members for code reviews

Use Cases

Email Validation

Test regex patterns for validating email addresses in registration forms and user input validation.

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

Phone Number Formatting

Create and test patterns for extracting or validating phone numbers in various formats.

Pattern: ^\+?1?\s*\(?\d{3}\)?[-\s]?\d{3}[-\s]?\d{4}$

Log File Parsing

Extract specific information from log files, such as timestamps, error codes, or IP addresses.

Pattern: \d{4}-\d{2}-\d{2}\s\d{2}:\d{2}:\d{2}

URL Extraction

Find and extract URLs from text content for link checking or content analysis.

Pattern: https?://[^\s]+

Code Refactoring

Search for specific code patterns when refactoring large codebases or performing bulk updates.

Pattern: function\s+\w+\s*\([^)]*\)

Data Cleaning

Identify and clean inconsistent data formats in CSV files or database exports.

Pattern: \b\d{1,3}(,\d{3})*(\.\d+)?\b

Code Examples

Email Validation

Validates email addresses with standard format

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

Phone Number (US)

Matches US phone numbers in various formats

regex 
^\+?1?\s*\(?([0-9]{3})\)?[-\s]?([0-9]{3})[-\s]?([0-9]{4})$

URL Matching

Matches HTTP and HTTPS URLs

regex 
https?://(?:www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b(?:[-a-zA-Z0-9()@:%_\+.~#?&/=]*)

Frequently Asked Questions

1 What are regex flags and when should I use them?
Regex flags are modifiers that change how the pattern matching works. The most common flags are: g (global) finds all matches instead of stopping after the first one; i (case-insensitive) matches regardless of letter case; m (multiline) makes ^ and $ match the start/end of each line rather than the entire string; s (dotall) allows . to match newline characters; and u (unicode) enables full Unicode matching. Use g when you need all occurrences, i for case-insensitive searches, and m when working with multi-line text.
2 How do I match special characters literally?
Special characters like . * + ? ^ $ ( ) [ ] { } | \ have special meanings in regex. To match them literally, escape them with a backslash. For example, to match a literal dot, use \. instead of just a dot. To match a dollar sign, use \$. The backslash itself also needs escaping as \\. Character classes can also help - [.] matches a literal dot without needing escaping.
3 What's the difference between .* and .+?
* means "zero or more" while + means "one or more" of the preceding element. So .* matches any character (.) zero or more times, including matching an empty string. .+ requires at least one character to match. Use .* when the pattern is optional, and .+ when you need at least one character. Both are greedy by default, meaning they match as much as possible - add ? after them (.*? or .+?) to make them non-greedy.
4 How do capture groups work?
Capture groups, created with parentheses ( ), extract portions of matched text for later use. For example, (\d{3})-(\d{4}) applied to "555-1234" creates two groups: group 1 captures "555" and group 2 captures "1234". You can reference these in replacement strings using $1, $2, etc., or access them programmatically. Use non-capturing groups (?:...) when you need grouping for quantifiers but don't want to capture the text.
5 Why doesn't my regex work in my programming language?
Different programming languages implement regex slightly differently. The most common issue is escaping - in many languages, backslashes in strings need double-escaping, so \d becomes "\\d" in the source code. Some languages have different flag syntax or don't support certain features like lookbehinds. Always check your language's regex documentation and remember to escape backslashes appropriately. Our tester uses JavaScript regex syntax, which is similar to but not identical to Python, PHP, or other languages.

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