It is likely impossible to completely define what is and isn't anti-Semitism and I will not try. I believe that there is a spectrum whereby some statements are very definitely anti-Semitic and others are very definitely not. In between lie a whole range of statements that may or may not be depending on numerous factors.
The Macpherson report recommended that "A racist incident is any incident which is perceived to be racist by the victim or any other person."
For the purposes of this blog I will follow that recommendation and post material I believe is likely to be perceived as anti-Semitic by others. That is not to say that I consider everything I post anti-Semitic, simply that I consider it likely that others will.
However, I will generally not post things I believe are definitely not anti-Semitic or that can be strongly argued not to be, even if it is likely that many will perceive it to be. Primarily this means that I will in general not consider statements about Israel or Zionists to be anti-Semitic unless their context or content indicate strongly that Jews are intended.