Test Regular Expressions Online in Real-Time
Validate patterns, find matches, and debug regex with instant feedback. Perfect for developers and programmers.
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A Regex Tester is a powerful online tool that allows developers and programmers to test regular expressions in real-time. Regular expressions (regex) are sequences of characters that define search patterns, mainly used for string matching and manipulation. This tool simplifies the process of validating, debugging, and understanding regex patterns.
See matches highlighted instantly as you type patterns and text
Test with all major regex flags (g, i, m, s, u, y)
Get comprehensive match information and statistics
Regular expressions (regex) are powerful tools for pattern matching in strings. They are used in almost every programming language and text editor for tasks like validation, searching, and replacing text. A regex consists of a sequence of characters that forms a search pattern.
Regex patterns consist of literal characters and metacharacters that define search criteria. Understanding these components is crucial for effective pattern matching:
| Component | Description | Example |
|---|---|---|
| Literals | Exact character matches | hello matches "hello" |
| Metacharacters | Special characters with meaning | ., *, +, ? |
| Character Classes | Matches any character in the set | [aeiou] matches any vowel |
| Quantifiers | Specify number of occurrences | a{2,4} matches "aa", "aaa", or "aaaa" |
| Anchors | Position-based matching | ^start matches "start" at beginning |
| Groups | Capture or group subpatterns | (abc)+ matches one or more "abc" |
When working with regular expressions, keep these performance considerations in mind:
Here are some frequently used regex patterns for common validation and extraction tasks:
Flags modify how regular expressions behave during matching. Here's what each flag does:
| Flag | Name | Description |
|---|---|---|
| g | Global | Find all matches rather than stopping after first match |
| i | Ignore Case | Case-insensitive matching |
| m | Multiline | Treat beginning and end characters (^ and $) as working over multiple lines |
| s | Dotall | Allow . to match newline characters |
| u | Unicode | Treat pattern as a sequence of Unicode code points |
| y | Sticky | Matches only from the index indicated by the lastIndex property |
Testing regular expressions with our online tool is simple and efficient:
Type your regular expression pattern in the input field. Don't include the forward slashes (/) as they are added automatically.
Choose the appropriate flags for your pattern by clicking on the flag options (g, i, m, etc.).
Enter the text you want to test your regex against in the text area.
Matches will be highlighted in green, and detailed match information will appear in the results panel.
Modify your pattern or text and see real-time updates to refine your regex.
Beyond basic pattern matching, regular expressions offer powerful features for complex text processing:
These zero-width assertions allow you to match patterns based on what comes before or after without including those characters in the match.
Groups allow you to extract specific parts of a match and apply quantifiers to multiple characters.
Modern regex engines support named groups for more readable and maintainable patterns.
This Regex Tester tool is built using modern web technologies to provide a fast and reliable testing experience:
Ensure user input conforms to expected formats like email addresses, phone numbers, or postal codes.
Extract specific information from structured or semi-structured text like log files or configuration data.
Perform complex find-and-replace operations across multiple files or large documents.
Identify patterns in source code for linting, refactoring, or automated analysis tools.
Greedy quantifiers (*, +, {n,m}) match as many characters as possible, while lazy quantifiers (*?, +?, {n,m}?) match as few as possible. For example, <.*> matches everything between the first < and last >, while <.*?> matches individual tags.
Use a backslash (\) before special characters to treat them as literals. For example, to match a literal dot, use \. To match a literal backslash, use \\.
Catastrophic backtracking occurs when a regex engine examines every possible combination of a pattern against text, leading to exponential time complexity. This often happens with nested quantifiers like (a+)+.
Yes! Enable the multiline flag (m) to make ^ and $ match the start and end of each line, not just the entire string. Also enable the dotall flag (s) if you want . to match newline characters.
Follow these guidelines to write effective and maintainable regular expressions:
Our online Regex Tester tool offers several advantages over other solutions:
Here's a collection of useful regex patterns for common tasks:
| Task | Pattern | Description |
|---|---|---|
\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b |
Basic email validation pattern | |
| URL | https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*) |
HTTP/HTTPS URL matching |
| Phone (US) | \(?\b[0-9]{3}\)?[-.]?[0-9]{3}[-.]?[0-9]{4}\b |
US phone number formats |
| Password Strength | ^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$ |
At least 8 chars, 1 uppercase, 1 lowercase, 1 number, 1 special char |
| IP Address | \b(?:[0-9]{1,3}\.){3}[0-9]{1,3}\b |
Basic IPv4 address matching |
| Hex Color | #([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3}) |
CSS hex color codes (#FFF or #FFFFFF) |
The Regex Tester is an invaluable tool for developers, data analysts, and anyone who works with text processing. By providing a simple interface for testing and validating regular expressions, it accelerates development workflows and helps ensure accurate pattern matching.
Whether you're validating user input, parsing log files, or performing complex text transformations, this tool provides everything you need to test and refine your regex patterns quickly and efficiently. Remember to always test your patterns with various inputs to ensure they work as expected in production environments.
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