A well-known URI is a Uniform Resource Identifier for URL path prefixes that start with /.well-known/.
The metadata is useful for various tasks, including directing a web user to use a mobile app instead of the website or indicating the different ways that the site can be secured.
The way to declare the different metadata requests that can be provided is standardized by the IETF so that other developers know how to find and use this information.
[1] Information shared by a web site as a well-known service is expected to meet a specific standard.
Specifications that need to define a resource for such site-wide metadata can register their nnh use with The list below describes known standards for .well-known services that a web server can implement.