How to determine checksum info on games without editors?

I’m tired of running into games that nobody cared to make editors for. What does it take to determine the type of checksum, etc? Why have I not seen any tutorials on this? Do I really have to get a JTAG/RGH box and hack the games that way to get saves modified the way I want? I do kind of miss the Gameshark Pro days on N64 hacking codes via PC connection. Hell, I helped write the tools people are using to do it on PS2. There’s a lot more RAM to be searching on newer games though. Seems like save editing might be faster, since all the data worth editing is right there in a few MB.