Regex Tester Tool
Test and debug your regular expressions in real-time with our powerful online tester
Match Results
Enter a regex pattern and test text to see matches
Match Details
Detailed match information will appear here
Master Regular Expressions
What is Regex?
Regular expressions (regex) are powerful patterns used to match character combinations in strings. They're essential for text processing, validation, and data extraction in programming.
How to Use This Tool
Enter your regex pattern in the first field, add your test text, and see matches in real-time. Use flags to modify matching behavior (global, case-insensitive, etc.).
Validate emails/URLs, extract data from text, search/replace operations, input validation, log file analysis, and text processing in programming languages.
Regular Expressions Explained
The Power of Pattern Matching
Regular expressions provide a concise and flexible means to match strings of text. A regex pattern describes a search pattern that can match, locate, and manage text. Our regex tester helps you visualize these matches instantly, showing exactly what your pattern will match in your test text.
Modern regex implementations include features like lookaheads, backreferences, and named capture groups that make them incredibly powerful for complex text processing tasks. Whether you're validating user input, parsing logs, or transforming data, regex is an indispensable tool in a developer's toolkit.
Essential Regex Syntax
Here are some fundamental regex components you can test with our tool:
- Literals:
/hello/matches "hello" exactly - Character classes:
[A-Za-z]matches any single letter - Quantifiers:
a{2,4}matches 2 to 4 "a" characters - Anchors:
^startandend$match start/end of string - Alternation:
cat|dogmatches "cat" or "dog"
Advanced Features
Our regex tester supports advanced features including:
- Capture groups:
(abc)captures matched text for reference - Lookaheads:
a(?=b)matches "a" only if followed by "b" - Backreferences:
(\w)\1matches repeated characters - Non-capturing groups:
(?:abc)groups without capturing - Unicode:
\p{Letter}matches letters in any language
Try these patterns in our tester to see how they work with your text!
Regex Tester FAQs
Different programming languages and tools implement regex with slight variations. Our tester uses JavaScript's regex engine (ECMAScript standard). Key differences between flavors include syntax for lookbehinds, named capture groups, and atomic grouping. Always test your regex in the environment where it will be used.
A basic email regex pattern looks like: ^[^\s@]+@[^\s@]+\.[^\s@]+$. This matches most common email formats but for production use, consider more comprehensive patterns that handle special cases. Test it in our tool with sample emails to verify its behavior.
Common issues include: not escaping special characters (. matches any character unless escaped as \.), incorrect quantifier placement, or misunderstanding greedy vs lazy matching. Use our tool's match highlighting to see exactly what your pattern matches.
Flags modify how the regex engine interprets your pattern:
g (global): Find all matches rather than stopping after first
i (ignore case): Case-insensitive matching
m (multiline): ^ and $ match start/end of each line
Toggle these flags in our tool to see their effects on your matches.
While our tool doesn't measure performance directly, you can identify potential performance issues by testing with large texts. Avoid patterns with excessive backtracking like nested quantifiers ((a+)+). For complex patterns, consider using atomic groups or possessive quantifiers where supported.