How can I find the appID locally?

[Tyrion]

All Steam games have an appID and I was wondering if some file or folder contains the ID somewhere?

[Kargor]

The quickest way is to go to the shop page -- the number that's in the URL is the AppID. Obviously, this also works for games you don't currently have installed, or games that you don't even own.

Also, the "Steam\steamapps" folder has "appmanifest_.*acf" files. Problem is, you need to read them to know which game they describe.

[Hitman]

This is not accurate. None of the "AppID" folders match the game I own.

[Yujah]

For games in your library: in the client, <rightclick> -> Properties -> Updates. App/Build ID are at the bottom.

[Steven]

This thread was quite old before the recent post, so we're locking it to prevent confusion.