Regex Tester

Test and debug regular expressions with real-time matching. See matches highlighted and understand how your patterns work.

100% client-side No signup Free forever
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Results

0 matches

Common Patterns

// reference

Regex Cheatsheet

Character Classes . Any character
\d Digit (0-9)
\w Word char (a-z, A-Z, 0-9, _)
\s Whitespace
[abc] Any of a, b, or c
[^abc] Not a, b, or c
Quantifiers * 0 or more
+ 1 or more
? 0 or 1
{n} Exactly n
{n,m} Between n and m
Anchors ^ Start of string
$ End of string
\b Word boundary
Groups (abc) Capture group
(?:abc) Non-capturing
a|b a or b
// how to use

How to Use Regex Tester

How to Use the Regex Tester

  1. Enter your regex: Type your regular expression pattern in the pattern field.
  2. Select flags: Enable global (g), case-insensitive (i), multiline (m), etc.
  3. Enter test text: Paste or type the text you want to test against.
  4. View matches: Matches are highlighted in real-time as you type.
  5. Check groups: See captured groups and their values in the match details.
  6. Use the cheatsheet: Reference common patterns and syntax.

Regex Tips

  • Start simple and build complexity gradually
  • Use non-greedy quantifiers (*?, +?) when appropriate
  • Test with edge cases (empty strings, special characters)
  • Consider performance with very long texts
  • Remember that regex syntax can vary slightly between languages
// features

Features

  • Real-time pattern matching
  • Match highlighting in test text
  • Capture group display
  • All regex flags supported (g, i, m, s, u)
  • Pattern explanation/breakdown
  • Common patterns library
  • Regex cheatsheet reference
  • Match count and positions
  • Replace functionality
  • JavaScript regex flavor
  • Export pattern with code
  • No registration required
// about

About Regex Tester

Regular expressions are incredibly powerful but notoriously difficult to write correctly. A single character can completely change what a pattern matches. Our Regex Tester provides instant visual feedback so you can develop and debug patterns with confidence.

Testing Features

The tester provides comprehensive regex debugging:

  • Real-time matching: See matches highlight instantly as you type
  • Match details: View captured groups, match positions, and counts
  • Flag support: Test with global, case-insensitive, multiline, and other flags
  • Replace preview: See replacement results before applying to real data

Learning Through Experimentation

The best way to learn regex is by experimenting. Start with simple patterns and progressively add complexity. The immediate visual feedback helps you understand how quantifiers, character classes, and groups work together.

Common Regex Patterns

Email validation, URL matching, phone number extraction, data parsing—these common tasks all rely on well-crafted regular expressions. Test your patterns against edge cases: What about international phone numbers? URLs with ports and query strings? Edge cases reveal regex weaknesses.

Avoiding Common Pitfalls

Regex mistakes often involve greedy quantifiers matching too much, forgetting to escape special characters, or incorrect anchoring. Testing with varied sample data helps catch these issues before your pattern reaches production code.

// faq

Frequently Asked Questions

What is a regular expression (regex)?
A regex is a pattern that describes a set of strings. It uses special syntax to match text: "\d+" matches one or more digits, "[A-Z]" matches uppercase letters. Regex is used for search, validation, text extraction, and find-replace operations in programming.
What regex flavors are supported?
We support JavaScript (web standard), PCRE (PHP, many languages), Python, Java, .NET, and POSIX regex. Flavors differ in features and syntax. Select your target language for accurate testing - a pattern working in one flavor may fail in another.
How do I debug why my regex isn't matching?
Our tester highlights matches in real-time and shows step-by-step matching. Enable "Explain" mode for plain-English description of what each part does. Common issues: forgetting to escape special characters, missing anchors, or incorrect quantifiers.
What are capture groups and how do I use them?
Parentheses create capture groups that "remember" matched text. Pattern "(\d{3})-(\d{4})" on "555-1234" captures "555" and "1234" separately. Use for extraction, backreferences, or in replacements. Our tester shows all captured groups clearly.
How do I match across multiple lines?
By default, ^ and $ match string start/end. Enable multiline mode (m flag) to match line start/end. The dot (.) doesn't match newlines unless you enable dotall mode (s flag). Flags significantly change regex behavior - our tool explains each flag.
Can I generate regex patterns automatically?
Yes! Paste example strings you want to match, and we'll suggest patterns that match them. This helps build patterns for emails, URLs, phone numbers, or custom formats. Generated patterns are starting points - refine them for your exact needs.