That just means it’s not a well-defined function (i.e. each input is mapped to only one unique output, which is not the case here). As other posters write, “id

That just means it’s not a well-defined function (i.e. each input is mapped to only one unique output, which is not the case here). As other posters write, “idempotent” means that recursively applying the function returns the same result, e.g. f(f(x)) = f(x). (The site is also indeed not idempotent, since entering a shady URL will not return the same shady URL.)