You should limit your keywords to a maximum of 1,024 characters including spaces. The Meta Keywords tag is intended to contain keywords or key phrases that you think people potentially interested in your site might be searching for at the engines. Each word or phrase should be separated by a comma followed by a single space. Some word repetition is permissible but don't push your luck - many engines are actually penalizing sites which overuse keywords. Excessive keyword repetition can result in your pages getting lower relevancy to searches, or being banned from the search engine altogether.
Some search engines are sensitive to line breaks, so make sure each meta tag is free of line breaks.
Paddy tried to think of all of the search phrases that a potential customer might use to try to track down irish potter on the Internet. Although it is not necessary to include both meta tags it is recommended that you do. Meta Tag Tips Don't put every word you can think of in your keyword tag. Search engines can penalize you for this by giving you poor rankings. Don't put words in your keyword tag that have nothing to do with your site.