Free Tool
Regex Tester
Test regular expressions with live match highlighting. Supports all standard flags, shows match positions, values, and capture groups — free, no sign-up, runs in your browser.
Regular Expression Tester
//g
Flags:
What is a regex tester?
A regular expression is a pattern that describes a set of strings. Common elements: . matches any character, \d matches digits, + means one or more, * means zero or more, and ^/$ anchor to start and end of a line.
Flags
The g flag finds all matches (not just the first). i makes matching case-insensitive. m makes ^ and $ match line starts and ends. s makes . match newlines.
Greedy vs lazy
Quantifiers like + and * are greedy by default — they match as much as possible. Adding ? makes them lazy: +? matches as little as possible. This matters when matching between delimiters.
How to use
- Enter your regular expression in the pattern field.
- Select any flags you need — g (global), i (case-insensitive), m (multiline), or s (dotall).
- Paste your test string in the input area. Matches are highlighted live and listed below with their index and captured groups.
Examples
- Simple: Pattern
\d+with flaggagainst"order 42 has 3 items"→ two matches:42at index 6 and3at index 15. - Developer workflow: Validate email format with
^[\w.-]+@[\w.-]+\.\w{ 2,}$. Test edge cases like[email protected](should match) anduser@domain(should not) before adding the pattern to your validator. - Edge case:
.*in<tag>content</tag>is greedy and matches the entire string from the first<to the last>. Use.*?to match lazily between the nearest delimiters instead.
Frequently Asked Questions
- What is a regular expression?
- A regular expression (regex) is a sequence of characters that defines a search pattern. Used in programming and text processing to find, match, and manipulate strings. They are supported in nearly every programming language.
- What do regex flags do?
- Flags modify how a regex pattern is applied: g (global) finds all matches instead of just the first; i (case-insensitive) matches regardless of letter case; m (multiline) makes ^ and $ match line boundaries; s (dotall) makes the dot . match newlines too.
- How do I match capture groups in regex?
- Use parentheses to create capture groups: (\d+) captures one or more digits. This tool shows each capture group value in the match details. Named groups use (?<name>pattern) syntax.
- What regex engine does this use?
- This tool uses the JavaScript built-in RegExp engine, which implements a subset of PCRE-style regex syntax. It supports lookahead, lookbehind (in modern browsers), named groups, and most standard regex features.