Free Online Regex Tester and Debugger
Regular expressions are one of the most powerful tools in a developer's toolkit — and one of the most frustrating to get right. Our free online regex tester lets you write, test, and debug regular expressions in real time. Type a pattern, paste your test string, and see matches highlighted instantly. No more guessing, no more trial-and-error deploys.
Whether you are validating email addresses, parsing log files, or extracting data from structured text, this tool gives you immediate visual feedback on what your regex matches — and what it misses.
How to Use the Regex Tester
Enter your regular expression pattern in the pattern field. Paste the text you want to test against in the text area. Matches are highlighted in real time as you type. You can add flags like global (g), case-insensitive (i), and multiline (m) to modify matching behavior. The tool shows you all matches, including capture groups.
Why Use a Regex Tester?
- Developers write and validate regex patterns before adding them to production code.
- Data engineers build extraction patterns for ETL pipelines and data cleaning.
- QA engineers test input validation patterns for forms and APIs.
- System administrators write log parsing patterns and search filters.
- Students learn regex syntax with immediate visual feedback.
Key Features
- Real-time match highlighting as you type
- Support for regex flags (global, case-insensitive, multiline)
- Shows capture groups and match details
- Clear error messages for invalid patterns
- 100% browser-based — private and secure
Common Regex Patterns
Here are a few useful patterns to get started: ^\S+@\S+\.\S+$ for basic email validation, \d{3}-\d{3}-\d{4} for US phone numbers, and https?:\/\/[^\s]+ for matching URLs. Test these in the tool above to see how they work, then modify them for your specific use case.
Frequently Asked Questions
What are regex flags?
Flags modify how a regex pattern is applied. The "g" (global) flag matches all occurrences instead of stopping at the first. The "i" flag makes matching case-insensitive. The "m" (multiline) flag makes ^ and $ match the start/end of each line, not just the entire string.
What is a capture group?
A capture group is a portion of your regex enclosed in parentheses (). It lets you extract specific parts of a match. For example, in the pattern (\d+)-(\d+), each set of digits is captured separately and can be referenced individually.
Does this tester use the JavaScript regex engine?
Yes. This tool uses the JavaScript (ECMAScript) regular expression engine, which is the same engine used in Node.js and all modern browsers. Patterns may behave slightly differently in other languages like Python, Java, or .NET that use different regex engines.
How do I match a literal dot or bracket?
Special characters like . [ ] ( ) must be escaped with a backslash to match them literally. For example, use \. to match an actual period, or \[ to match a literal opening bracket.