What are App Domains in Facebook Apps?

Question

the app domain is your domain name.

Before you enter your domain, first click on Add Platform, select website, enter your site URL and mobile site url. Save the settings.

Thereafter, you can enter the domain name in the App domains field.

See more at my blog: http://www.ogbongeblog.com/2014/03/unable-to-add-app-domains-to-new.html

To add to the answers above, the App Domain is required for security reasons. For example, your app has been sending the browser to "www.example.com/PAGE_NAME_HERE", but suddenly a third party application (or something else) sends the user to "www.supposedlymaliciouswebsite.com/PAGE_HERE", then a 191 error is thrown saying that this wasn't part of the app domains you listed in your Facebook application settings.

If you don't specify the platform for the app you won't able to add app domain correctly.

Here is an example -- validate that its a type a website platform.

In this example:

http://www.example.com:80/somepage?parameter1="hello"&parameter2="world"

the bold part is the Domainname. 80 is rarely included. I post it since many people may wonder if 3000 or some other port is part of the domain if their not staging their app for production yet. Normally you don't specify it since 80 is the default, but if you just want to specify localhost just do it without the port number, it works just as fine. The adress, though, should be http://localhost:3000 (if you have it on that port).