As of February 14th 2024, RFC 9512opens in a new tab formally registers application/yaml as the media type for all YAML content, and adds +yaml as a standard structured suffix for all YAML-based more specific media types. Media type structured suffixes like this ( +xml and +json are other common examples) are used to define specific types for content that's based on an existing generic content type (such as YAML). The full RFCopens in a new tab is well worth a read if you're interested in the finer details, and discusses all sorts of more detailed questions around interoperability for an evolving language like YAML, its relationship with JSON, and the (many) security considerations to be aware of when defining a formal API around YAML data.