When using the MyFonts API, you must always properly attribute MyFonts as the source of the displayed content to MyFonts (see Branding Guidelines for more info), and you must link back to the appropriate canonical page on MyFonts. Font creators rely on the exposure your app will provide, but it has to be done properly.
When using the MyFonts API, you must not replicate the core MyFonts experience. This would become redundant and confusing to users. We reserve the right to review apps that conflict with the interests of MyFonts and/or its suppliers, or with the stability of our servers and infrastructure. We also reserve the right to terminate use of the API for any reason.
Caching of MyFonts API data is encouraged, but you must not cache data for longer than specified in the API HTTP response headers.
The MyFonts API is for non-commercial use. It should be used to assist our efforts: to help people find, try, and buy fonts. If you have a commercial implementation in mind, please contact us.