Yes here I would use a comma or a space as well. Do not use a . # or @ sign. This will trip up your database big time if you're going to use these as your delimiters. The . character can give you some flexibility in other scenarios, but usually keywords are not ended with a period.
Commas as delimiters, in certain contexts can be bad too, for example, let's say in the middle of a sentence wherein there is a break in continuity in the text, but it depends on your deployment of such delimiters. But since you're just talking about keywords, you can use the comma as the delimiter here.
It's almost unheard of to have in a keyword, a comma. If your keyword is a comma, that's a problem. That can easily be fixed by defaulting to a space delimiter:
- In that instance, if you want to use the comma as the delimiter, then you have to specify to the user that an extra input will be needed, ergo not making the comma the delimiter.
This is probably the best solution, because with spaces, there are intrinsically no keywords that are entirely blank spaces.
I was thinking of another solution, but it would probably be a waste of time because it doesn't really make sense to search up a comma as a keyword as a singular character.