Master Regular Expressions with our Regex Tester
Regular Expressions (Regex) are an incredibly powerful syntax used by developers, data scientists, and IT professionals to search, validate, and extract patterns from text strings. However, writing regex can be notoriously difficult due to its dense and cryptic syntax.
Our free online Regex Tester & Debugger takes the guesswork out of pattern matching. By providing a real-time testing environment, you can instantly see exactly what your expression is capturing. Whether you are validating email addresses, extracting phone numbers, or parsing server logs, this tool highlights matches instantly and extracts them into a clean, copyable list.
How to Test a Regex Pattern
- 1Enter your PatternType your regular expression into the pattern input box. Do not include the starting and ending forward slashes (`/`), as the tool handles them automatically.
- 2Configure FlagsToggle the switches below the pattern to apply Global (g), Ignore Case (i), Multiline (m), or DotAll (s) behaviors to your search.
- 3Add Test StringPaste the block of text, code, or logs you want to search through into the "Test String" area.
- 4Review ResultsWatch the right panel update instantly. See visual highlights in context, and copy individual extracted matches from the list below.
Key Features
- 100% Client-Side PrivacyRegex testing happens natively inside your web browser. Your sensitive logs, passwords, or PII are never uploaded to a server.
- Real-Time EvaluationNo need to hit a "Run" button. The engine evaluates your keystrokes instantly, providing immediate feedback on syntax errors or matched strings.
- Modern JS Regex EngineUtilizes the standard JavaScript RegExp implementation, ensuring full support for modern features like look-aheads and capture groups.
Frequently Asked Questions
Common questions about regular expressions, syntax rules, and tool functionality.
Which regex flavor does this tool use?
This tool runs on the standard JavaScript RegExp engine embedded in modern browsers. It supports ECMA-262 specifications, which closely mirrors PCRE (Perl Compatible Regular Expressions) but with minor differences in advanced lookbehind capabilities depending on browser versions.
What are regex flags?
Flags are optional modifiers that change how the search operates. For example, the Global (g) flag tells the engine to find all matches instead of stopping at the first one. The Ignore Case (i) flag makes the search case-insensitive.
Why is my pattern showing an error?
Errors typically occur due to invalid syntax. Common mistakes include unclosed character classes (e.g., missing a closing bracket `]`), unescaped special characters (like trying to match a literal `?` without typing `\?`), or invalid group references.
How do I escape special characters?
If you want to match a character that usually has a special meaning in regex (such as `. * + ? ^ $ ( ) | [ ] \`), you must precede it with a backslash `\`. For example, to match a literal dollar sign, type `\$`.