Question 1

What regex syntax does this tool support?

Accepted Answer

This tool supports JavaScript regular expression syntax, which is widely used in web development. It supports flags like g (global), i (case-insensitive), m (multiline), s (dotAll), and u (unicode).

Question 2

How do I capture groups in my regex?

Accepted Answer

Use parentheses () to create capture groups. Matched groups are displayed below the results. For example, (\d+)-(\d+) will capture two number groups separated by a hyphen.

Question 3

What are regex flags?

Accepted Answer

Flags modify how the regex engine searches. g = global (find all matches), i = case-insensitive, m = multiline (^ and $ match line boundaries), s = dotAll (. matches newlines), u = unicode mode.

Question 4

Why is my regex not matching?

Accepted Answer

Common issues include: missing escape characters for special chars like . * + ?, incorrect anchors, or wrong flag settings. Check the error message displayed below the pattern input for syntax errors.

Question 5

How do I match special characters?

Accepted Answer

Escape special characters with a backslash. For example, \. matches a literal dot, \* matches a literal asterisk, and \? matches a literal question mark.

Question 6

What is the difference between greedy and lazy quantifiers?

Accepted Answer

Greedy quantifiers (*, +, ?, {}) match as much as possible, while lazy quantifiers (*?, +?, ??, {}?) match as little as possible. For example, <.*> matches the entire string, while <.*?> matches the shortest possible tag.

Question 7

How do I use character classes?

Accepted Answer

Character classes [abc] match any single character in the brackets. You can use ranges like [a-z] for lowercase letters, [0-9] for digits, or [^abc] to negate (match anything except a, b, or c).

Question 8

Can I test multiple patterns at once?

Accepted Answer

No, this tool tests one pattern at a time. However, you can quickly switch between patterns and test strings to compare results.

Question 9

Does this tool support lookaheads and lookbehinds?

Accepted Answer

Yes, JavaScript regex supports positive lookahead (?=), negative lookahead (?!), positive lookbehind (?<=), and negative lookbehind (?<!) assertions.

Question 10

How do I match unicode characters?

Accepted Answer

Use the u flag to enable unicode mode. Then you can use \u{XXXX} syntax for unicode code points, or character properties like \p{Letter} to match any letter in any language.

Question 11

What are anchors in regex?

Accepted Answer

Anners are zero-width assertions that match positions, not characters. ^ matches the start of a line (or string), $ matches the end, \b matches word boundaries, and \B matches non-word boundaries.

Question 12

How do I replace matched text?

Accepted Answer

Switch to the Replace tab and enter your replacement pattern. You can use $1, $2, etc. to reference captured groups. The replacement is applied to all matches when using the g flag.

Regex Tester

How to Use Regex Tester