hello i have a zip file for a attinymegacore for some attiny boards. normally i get a json link i add to the board manger URL. However the site i got it from was a year ago and is no longer there. I do however have a copy of the files for it. I was wondering how can i manually add this to the board manger is there a step by step guide?
You can find the location of "" in the Arduino IDE's File > Preferences ("Sketchbook location").
The others depend on the specific boards platform you are using. "" can probably be any unique name you can come up with (e.g., "foobar"). It's very important to get right though. Depending on which ATtinys the boards platform is for, it could either be avr (for the classic ATtinys like ATtiny85) or megaavr (for the modern ATtinys like ATtiny3217).