Regex to Match Percentages

This regex matches percentage values in standard notation. Here is the token-by-token breakdown:

^ — Anchors the match at the start of the string to ensure the entire input is a percentage.

-? — Matches an optional minus sign. Negative percentages are valid in many contexts, such as financial losses or negative growth rates.

\d+ — Matches one or more digits for the whole number part. The \d shorthand matches digits 0-9 and the + requires at least one.

(?:.\d+)? — An optional non-capturing group matching a decimal point followed by one or more digits. This allows both whole number percentages like '50%' and decimal percentages like '99.9%'. The entire group is optional.

% — Matches a literal percent sign at the end. This character is not a regex metacharacter, so it does not need escaping.

$ — Anchors the match at the end of the string.

This pattern validates percentage values commonly found in statistics, financial data, CSS properties, and user interfaces. It matches values like '100%', '3.14%', '-5%', and '0.1%'. Note that it does not restrict the range to 0-100, since percentages above 100% (like '150%' for zoom levels) and below 0% are valid in many applications. If you need to restrict the range, you would need additional logic in your application code or a more complex regex with numeric alternation similar to the port number pattern.