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Regex Tester

Test and debug regular expressions with pattern matching, highlighting, and explanations

Interactive tool

What is a Regex Tester?

A regex tester is a tool that helps you write, test, and debug regular expressions (regex). It shows you which parts of your text match your pattern, highlights matches in real-time, and provides explanations of regex syntax. Perfect for developers who need to validate and refine regex patterns before using them in code.

How to Use This Regex Tester

  1. 1Enter your regular expression pattern in the pattern field
  2. 2Type or paste the text you want to test against in the test string field
  3. 3Select the regex flags you need (global, case insensitive, multiline, etc.)
  4. 4See matches highlighted in real-time as you type
  5. 5View match details including position, captured groups, and count
  6. 6Read the pattern explanation to understand how your regex works
What you get

Key features

Real-Time Testing

See matches instantly as you type your pattern or test string

Match Highlighting

Visual highlighting of all matches in the test string

Pattern Explanation

Get automatic explanations of your regex pattern

All JavaScript Flags

Support for g, i, m, s, u, and y flags

Capture Groups

View named and numbered capture groups for each match

Error Detection

Clear error messages for invalid regex patterns

100% Private

All testing happens locally in your browser

Free Forever

No registration, no limits, completely free

Why Use a Regex Tester?

Regular expressions are powerful but can be tricky to write correctly. A regex tester lets you validate your patterns before deploying them to production, saving time debugging and preventing errors. Visual feedback shows exactly what your pattern matches, making it easier to refine and optimize your regex. Perfect for form validation, text parsing, data extraction, and search and replace operations.

Common use cases

  • Validating email addresses, phone numbers, and URLs
  • Extracting data from log files or structured text
  • Form input validation in web applications
  • Search and replace operations in code editors
  • Parsing configuration files and data formats
  • Text cleaning and data transformation
  • URL routing and pattern matching
  • Syntax highlighting and lexical analysis

Regex Flags Explained

  • g (global): Find all matches instead of stopping after the first match
  • i (case insensitive): Match both uppercase and lowercase letters
  • m (multiline): ^ and $ match line boundaries instead of string boundaries
  • s (dotAll): . matches newline characters as well as other characters
  • u (unicode): Enable full unicode support for patterns
  • y (sticky): Match only from the lastIndex position

Common Regex Patterns

Some frequently used patterns include: \d+ for numbers, [a-zA-Z]+ for words, \s+ for whitespace, ^\w+@\w+\.\w+$ for email addresses (basic), and \b\w{3,}\b for words with 3 or more characters. These building blocks can be combined to create more complex patterns.

Pro tips

Tips & best practices

Use the global flag for multiple matches

Enable the g flag to find all occurrences in the text instead of just the first match.

Test edge cases thoroughly

Try empty strings, special characters, and boundary conditions to ensure your regex handles all scenarios.

Escape special characters

Use backslash to escape characters with special meaning: . * + ? ^ $ { } [ ] ( ) | \

Keep patterns simple

Complex regex can be hard to maintain. Break down complicated patterns into smaller, testable parts.

Use non-capturing groups when appropriate

Use (?:...) instead of (...) when you need grouping but not capture, improving performance.

Built for trust

Privacy & security

This regex tester runs entirely in your web browser using native JavaScript RegExp. Your patterns and test strings never leave your device. All processing happens locally with no server communication.

Related tools

Frequently Asked Questions

What is a regular expression (regex)?

A regular expression is a sequence of characters that defines a search pattern. It is used for pattern matching within strings, allowing you to search, validate, and manipulate text based on specific rules. Regex is supported in most programming languages and text editors.

How do I test a regex pattern?

Enter your regex pattern in the pattern field, provide the text you want to test in the test string field, and select any flags you need (like global or case insensitive). The tool will instantly show you all matches, highlight them in the text, and provide details about each match including position and captured groups.

What are regex flags and when should I use them?

Regex flags modify how the pattern matching works. The global (g) flag finds all matches instead of just the first one. The case insensitive (i) flag ignores uppercase and lowercase differences. The multiline (m) flag makes ^ and $ match line boundaries. The dotAll (s) flag allows the dot to match newline characters. Choose flags based on your specific matching requirements.

What are capture groups in regex?

Capture groups are portions of the regex pattern enclosed in parentheses. They allow you to extract specific parts of a match for later use. For example, in the pattern (\d{3})-(\d{4}), the first group captures three digits and the second captures four digits. Our tool displays all captured groups for each match.

Why is my regex pattern not matching?

Common reasons include: forgetting to enable the global flag for multiple matches, not escaping special characters like dots or brackets, incorrect flag settings, or syntax errors in the pattern. Check the explanation tab to understand what your pattern does, and verify that special characters are properly escaped with backslashes.

Is my regex pattern and test data private?

Yes, completely private. This regex tester runs entirely in your browser using native JavaScript. Your patterns and test strings never leave your device. No data is sent to any server or stored anywhere. All processing happens locally on your machine.