Regex Tester
Test and debug your regular expressions in real-time with our free online Regex Tester. Whether you are a developer writing pattern-matching code, a data analyst extracting information from text, or a system administrator configuring log filters, this tool provides instant feedback on your regex patterns. Simply enter your regular expression, provide a test string, and immediately see all matches highlighted with detailed group captures. The tool supports all standard regex features including character classes, quantifiers, anchors, lookaheads, backreferences, and flags. Get helpful error messages when your pattern has syntax errors, and use the built-in regex reference guide for quick syntax lookups. No more guessing whether your pattern works — see results instantly and iterate until your regex is perfect.
What Is
A regex tester is a development tool that allows you to write, test, and debug regular expressions (regex) against sample text in real-time. Regular expressions are powerful pattern-matching sequences used across virtually every programming language for tasks like input validation, text search and replace, data extraction, log parsing, and string manipulation. Writing regex patterns can be challenging even for experienced developers because the syntax is compact and a single misplaced character can completely change the pattern's behavior. A good regex tester solves this by providing instant visual feedback: it highlights all matches in your test text, shows capture group contents, displays match positions, and explains what each part of your pattern matches. Our free online Regex Tester goes further with features like syntax error detection, a built-in regex quick reference, support for multiple regex flavors and flags (global, case-insensitive, multiline, and dot-all), and real-time match highlighting as you type. It is an indispensable tool for anyone working with text processing, data validation, or pattern matching in their code.
How to Use
- Enter your regular expression pattern in the regex input field. Include the pattern between forward slashes or enter it directly without delimiters.
- Type or paste your test string in the text area where you want to search for pattern matches.
- Set the desired flags such as global (g), case-insensitive (i), multiline (m), or dot-all (s) to control how the pattern is applied.
- View the highlighted matches in your test text and examine the detailed match information including capture groups and positions.
- Read any error messages if your regex has syntax errors, then adjust your pattern and test again until you get the desired results.
Examples
Input: Pattern: ^\d{3}-\d{4}$, Input: 555-1234
Process: Match start anchor → 3 digits → hyphen → 4 digits → end anchor
Result: ✓ Match: 555-1234 (full match)
Input: Pattern: (\w+)@(\w+\.\w+), Input: [email protected] (with groups)
Process: Capture group 1 (\w+) → @ → Group 2 (\w+\.\w+)
Result: ✓ Match, Group1: test, Group2: email.com
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Frequently Asked Questions
What is a regular expression?
A regular expression (regex or regexp) is a sequence of characters that defines a search pattern. These patterns are used for string matching, validation, search-and-replace operations, and data extraction. Regular expressions are supported by virtually all programming languages including JavaScript, Python, Java, PHP, Ruby, C#, and many others. They provide a concise and flexible way to match text patterns ranging from simple character sequences to complex multi-line formats.
What regex flavors does this tool support?
This regex tester primarily supports the JavaScript regex engine (ECMAScript standard), which is one of the most widely used regex flavors. This includes support for character classes, quantifiers (greedy and lazy), anchors, groups, backreferences, lookaheads, lookbehinds, and named capture groups. If you need to test regex for other languages like Python, PHP, or Java, the JavaScript flavor is very similar for most common patterns, though there may be minor differences in advanced features.
How do I match special characters in regex?
To match special regex characters literally, you need to escape them with a backslash. The characters that require escaping are: . ^ $ * + ? { } [ ] \ | ( ). For example, to match a literal period, you would use \. in your pattern. To match a literal backslash, you use \\ . Most regex testers, including ours, will show you an error if you forget to escape a character that would otherwise be interpreted as a metacharacter.
What do the regex flags mean?
Regex flags modify how the pattern matching behaves. The global flag (g) makes the regex find all matches instead of stopping at the first one. The case-insensitive flag (i) makes the pattern match regardless of letter case. The multiline flag (m) changes ^ and $ to match the start and end of each line rather than the entire string. The dot-all flag (s) makes the dot (.) match newline characters as well. You can combine multiple flags like /pattern/gims to use them together.
Why is my regex not matching anything?
Common reasons for regex failing to match include: typos or syntax errors in the pattern, forgetting to escape special characters, case sensitivity when you meant it to be case-insensitive (add the i flag), anchors (^ or $) that do not match the expected position, or greedy quantifiers consuming more text than intended. Use the error messages and match highlighting in this tester to diagnose the issue. Start with a simple pattern and gradually add complexity while checking results at each step.