demo instructions in the cart itself, code and even spritesheet reasonably commented.
all tiles connect with each other by default, but that's changeable in the update_tile method.

feel free to make modifications, additions, optimisations, etc

made for a quite large and special sorta-secret project ;)

tool tools autotile tilemap

That's really cool! I'm always baffled by how many sprites are needed for auto tiling.

I often remember the Rpg Maker 2000 and how it included those features as if it was nothing. There also was an interesting simplicity to the way its autotiles worked - they needed less sprites and still worked perfectly. I wish modern tiling editors would work similarly, reducing the amount of tiles that need to be provided as graphics.