[2] JSON API は、 JSON を用いた Web API のデータ形式の1つです。 MIME型は application/vnd.api+json とされています。

[3] 大変紛らわしいことに、一般的に「JSON API」といえば JSON をデータ形式として使う任意の API のことを指していますが、ここでいう「JSON API」は固有名詞です。一般的な「JSON API」のほとんどは、ここでいう「JSON API」ではありません。 (悪意すら感じるネーミングですね。)

[1] JSON API :: A standard for building APIs in JSON. ( (2014-06-09 16:18:31 +09:00 版)) http://jsonapi.org/

[4] JSON API — Latest Specification (v1.0) (2015-11-16 23:46:06 +09:00 版) http://jsonapi.org/format/

[5]

JSON API — JSON Patch Extension (2016-03-20 23:22:07 +09:00 版) http://jsonapi.org/extensions/jsonpatch/

Content-Type: application/vnd.api+json; ext=jsonpatch
Accept: application/vnd.api+json; ext=jsonpatch

[6] (2013-07-22 15:39:05 +09:00 版) https://www.iana.org/assignments/media-types/application/vnd.api+json

Required parameters : none
Optional parameters :
none

[7]

JSON API — JSON Patch Extension (2016-03-20 23:22:07 +09:00 版) http://jsonapi.org/extensions/jsonpatch/

The server MUST specify a Content-Type header of application/vnd.api+json; ext=jsonpatch.

[8]

JSON API — Latest Specification (v1.0) (2016-03-20 23:22:07 +09:00 版) http://jsonapi.org/format/#content-negotiation-clients

Client Responsibilities
Clients MUST send all JSON API data in request documents with the header Content-Type: application/vnd.api+json without any media type parameters.
Clients that include the JSON API media type in their Accept header MUST specify the media type there at least once without any media type parameters.
Clients MUST ignore any parameters for the application/vnd.api+json media type received in the Content-Type header of response documents.
Server Responsibilities
Servers MUST send all JSON API data in response documents with the header Content-Type: application/vnd.api+json without any media type parameters.
Servers MUST respond with a 415 Unsupported Media Type status code if a request specifies the header Content-Type: application/vnd.api+json with any media type parameters.
Servers MUST respond with a 406 Not Acceptable status code if a request's Accept header contains the JSON API media type and all instances of that media type are modified with media type parameters.
Note: The content negotiation requirements exist to allow future versions of this specification to use media type parameters for extension negotiation and versioning.

[9] その後 JSON:API って書くようになったみたいですね。 (わかりにくいことはかわってないが。)