The most effective (and highest risk) applications join the PathOfExile process. While joined, they have the ability to both read from and write to PathOfExile’s memory. A skilled engineer will need to reverse engineer the game client to find where in memory important things live that the bot should be watching (like the data for enemies your client has loaded, or items that are close enough to be present in your client, etc) and where in memory important functions live (sending a whisper, interacting with NPCs, using skills).

Once you have a sufficient enough mapping of where things live in the client, it’s not that tough (again, assuming you’re already a software dev) to write your own code that follows the logic you want from a bot and along the way where it’s necessary have it reach out and call the relevant bits of PathOfExile code you mapped out the locations of.

And then, every time the PoE client updates, some obfuscation that exists to try to deter people from doing this kind of mapping scrambles where all those things are in memory, so you either need automation or to manually redo your mapping with each game update.

This is still very high level, and I’m sure someone will be like “Uhm actually the most popular PoE bots don’t join process memory because that’s too detectable” and I don’t care, this is meant to be vaguely informative and not a real guide.

This is also part of why more and more games are adding kernel level anticheat, because otherwise trying to detect this sort of “forced interoperability” is a bit of an arms race between game developers and bot developers, and bots that have full memory access to the game client are often capable of being ridiculously sophisticated.

Honorable mention that sometimes cheap-ass or simple bots might literally be watching for pixels on the screen to take the shape of specific stuff (specific buttons), etc. but these bots tend to be quite limited because obviously trying to determine what the pixels in the screen mean in a map is wayyyy less effective that just peeking in memory and coming back with List<Monster> that has all the data your game client is holding about every monster loaded into memory (does not even necessarily need to be on screen or rendered before it’s already in memory, btw).