The app settings for a function app are similar to the app settings you would configure for a website: in the app settings, you insert the global options that are valid for all of the functions contained in the function app.
When you develop an Azure Function, you can have local settings—that is, the settings you want to use only when you run your functions locally (for example, using the local storage emulator or a test key for a particular service)—and Azure settings—that is, the settings you want to run when you deploy your functions in a function app.
Moreover, you have settings that are related to the runtime (for example, the configured extensions, and the logger settings).
For the local settings, you can use a file called local.settings.json. This file is, generally, created by Azure Function Core Tools (or by Visual...