The mime-types library provides a library and registry for information about MIME content type definitions. It can be used to determine defined filename extensions for MIME types, or to use filename extensions to look up the likely MIME type definitions. This is release 2.99, the deprecation version of mime-types 2.x, where deprecation warnings are noisy and data that has been deprecated is now no longer available. The data is both dropped from the data files and is stubbed out as empty or +nil+ values as appropriate. mime-types-2.6 was the last version of mime-types 2.x with newly available features, and mime-types 2.99 will only receive quarterly updates to the IANA registered MIME media types plus any security updates that may be required. If the loss of the deprecated data matters, be sure to set your dependency appropriately: gem 'mime-types', '~> 2.6, < 2.99'