What is Regex Tester Online?
A regular expression (regex) is a sequence of characters defining a search pattern. They are used in nearly every programming language for string matching, validation, extraction, and replacement. Our regex tester online tool highlights every match in your test string in real-time as you type your pattern, supporting global, case-insensitive, and multiline flags. Regex is a powerful but often cryptic language. This tester simplifies the process by providing visual feedback on captures, groups, and indices. Whether you are validating email formats, stripping HTML tags, or parsing complex log files, this real-time sandbox lets you iterate quickly until your pattern is perfect. Because the regex engine runs directly in your browser's JavaScript environment, you can test patterns specifically as they will behave in your web or Node.js applications. This ensures that the results you see here are exactly what you will get in production.
How to Use Regex Tester Online
- Enter your regular expression pattern in the pattern field.
- Toggle flags (g for global, i for case-insensitive, m for multiline).
- Paste your test string below — matches are highlighted live.
- See match groups and indices in the details panel.
Example
Date format regex test
Input
/^\d{4}-\d{2}-\d{2}$/Output
2024-01-15 ✓ matchesDeveloper Tips
Regex is powerful but can be expensive. Avoid "Catastrophic Backtracking" by keeping your patterns as specific as possible. For complex logic, consider breaking the regex into smaller, readable parts or using a combination of string methods and regex.
Frequently Asked Questions
What does the "g" flag do in a regex?
The global flag makes the regex find all matches in the string, not just the first one. Without it, the engine stops after the first match.
What is a capturing group?
Parentheses () in a regex create a capturing group. The matched substring is stored separately and can be accessed via match[1], match[2], etc.