About Regex Tester
Writing a regular expression that works exactly as intended is notoriously tricky. Our free online Regex Tester lets you write a regex pattern and test it against sample text instantly, with all matches highlighted in real time. See match groups, position indices, and capture group values — everything you need to debug a regex without running your application.
Regular expressions are used in virtually every programming language for string matching, validation, parsing, and transformation. Common use cases: validating email addresses, phone numbers, and passwords; extracting data from log files; parsing structured text like CSVs or configuration files; and performing find-and-replace operations in code editors.
Our tester shows all matches highlighted inline in the test string, with a match table displaying each match's full value, position (start index, end index), and any named or numbered capture group values. Flags (global, case-insensitive, multiline, dotAll) are individually toggleable. The tool supports JavaScript regex syntax.
How to Use the Regex Tester
Enter your regex pattern
Type your pattern in the regex input field (without surrounding slashes).
Set flags
Toggle flags: g (global), i (case-insensitive), m (multiline), s (dotAll).
Enter test string
Paste or type the text you want to test the regex against.
View matches
Matches are highlighted in the test string. The match table shows full values, positions, and capture groups.
Key Features & Highlights
Common Use Cases
- Validate email address regex before shipping to production
- Debug regex patterns that aren't matching as expected
- Test log parsing patterns against sample log lines
- Build and verify form validation regexes
- Extract structured data from text using capture groups
- Test regex patterns for search-and-replace operations
Frequently Asked Questions
The tool uses JavaScript's built-in RegExp engine, which is standard ECMAScript regex. This is compatible with most modern regex syntax used in Python, PHP, Ruby, and other languages, with minor differences.
Escape special characters with a backslash: \. matches a literal dot, \* matches a literal asterisk, \( matches a literal parenthesis.
The global flag (g) makes the regex find ALL matches in the string. Without it, only the first match is returned. Always use g when you want to find every occurrence.
Yes, 100% free with no hidden fees, subscriptions, or account requirements.
Everything runs client-side directly inside your web browser. No files, texts, or parameters are sent to our servers.
Yes, our tools are fully responsive and work seamlessly on iPhones, iPads, Android smartphones, and tablets.