RegEx Tester

Test and debug regular expressions with real-time matching

Enter a pattern and test text to see matches

. - Any character
* - 0 or more
+ - 1 or more
? - 0 or 1
^ - Start of line
$ - End of line
\d - Digit
\w - Word char
\s - Whitespace
[abc] - Character class
(abc) - Group
a|b - Alternation

How to Use This Tool

1

Enter Regular Expression

Type your regex pattern in the input field. The tool validates syntax in real-time.

2

Configure Flags

Select regex flags like global (g), case-insensitive (i), multiline (m), etc. to modify matching behavior.

3

Provide Test Text

Enter the text you want to test against your pattern. Matches will be highlighted automatically.

4

Review Match Results

See all matches with their positions, captured groups, and execution time.

5

Use Common Patterns

Click preset patterns for common use cases like email, URL, phone number validation, etc.

Pro Tips

  • •Use the 'Escape as Pattern' button to convert your test text into a regex pattern that matches it literally
  • •The Pattern Analysis shows complexity and explains what your regex contains
  • •Highlighted matches show all occurrences with highlighting in the preview
  • •Named capture groups are displayed separately in the match results
  • •The Quick Reference panel provides common regex syntax at a glance
  • •Execution time helps you identify potentially slow regex patterns

Mastering Regular Expressions for Pattern Matching

Regular expressions (regex or regexp) are powerful pattern-matching tools used throughout programming for searching, validating, and manipulating text. This regex tester provides real-time pattern matching, helping developers debug complex expressions and understand how different flags affect matching behavior. Whether you're validating user input, parsing log files, or extracting data from text, understanding regex patterns is essential for efficient text processing and data validation in modern software development.

Key Features

Real-time regex pattern validation with syntax error detection

Interactive match highlighting showing all occurrences in test text

Support for all JavaScript regex flags (global, case-insensitive, multiline, etc.)

Common pattern library for emails, URLs, phone numbers, and more

Capture group extraction with named group support

Pattern complexity analysis and performance timing

Quick reference guide for regex syntax and metacharacters

One-click pattern escaping for literal text matching

Common Use Cases

Validating user input forms for email addresses, phone numbers, and postal codes with precise pattern matching

Extracting specific data from log files, CSV data, or unstructured text using capture groups

Search and replace operations in code editors and text processing applications

Building input masks and validation rules for web forms and applications

Parsing and analyzing structured data formats like URLs, file paths, and configuration files

Frequently Asked Questions

What's the difference between greedy and lazy quantifiers?

▼
Greedy quantifiers (*, +, ?) match as much text as possible, while lazy quantifiers (*?, +?, ??) match as little as possible. For example, in the text '<div>content</div>', the pattern '<.*>' greedily matches the entire string, while '<.*?>' lazily matches just '<div>'.

How do I match special characters literally?

▼
Special regex characters like . * + ? ^ $ { } ( ) | [ ] \ need to be escaped with a backslash to match literally. For example, to match a period, use \. instead of just . The 'Escape as Pattern' button automatically escapes all special characters in your text.

What are capture groups and how do I use them?

▼
Capture groups, defined with parentheses (), extract specific parts of a match. Numbered groups (1, 2, 3...) are accessed by order, while named groups (?<name>pattern) can be referenced by name. They're useful for extracting data like /(\d{4})-(\d{2})-(\d{2})/ to capture year, month, and day from a date.

Why isn't my regex matching across multiple lines?

▼
By default, ^ and $ match the start and end of the entire string, and . doesn't match newlines. Enable the multiline flag (m) to make ^ and $ match line boundaries, and the dotAll flag (s) to make . match newlines. This is essential for processing multi-line text like log files or documents.

How can I improve regex performance?

▼
Optimize regex performance by: 1) Being specific rather than using .* everywhere, 2) Using atomic groups and possessive quantifiers to prevent backtracking, 3) Anchoring patterns with ^ or $ when possible, 4) Avoiding nested quantifiers like (a+)*, and 5) Testing with representative data to identify slow patterns using the execution time display.