It is quite nuanced, but generally it depends on your intent. If you plan how to commit a crime without intending or encouraging anyone to commit it, that is not illegal, but intending to commit a crime, even if some else does the actual deed or if nobody is even harmed, that is illegal, as they were the perpetrator and succeeded. Eg https://law.stackexchange.com/questions/80382/can-you-be-pun...