Regex Editor & Tester

Searches for the number 12 as a standalone value in a comma- or space-separated list. Negative lookaheads ((?![0-9])) prevent matching 12 inside longer numbers like 123 or 512, with an optional surrounding character allowed for delimiters. A second alternative matches 12 at the very start of the string when followed by a comma or whitespace. Commonly used to check whether a specific ID or numeric value exists in a delimited list.