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. This tool highlights every match in your test string in real-time as you type your pattern, with flag support (g, i, m, s).
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 ✓ matchesFrequently 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.