The Japan Patent Office (JPO) has begun providing patent information on a trial basis using an application programming interface (API) from January 2022, with the aim of promoting the use of patent information held by the JPO.
With the API, it will be possible to obtain bibliographic information, progress information, and document substance (the text of submitted documents such as notices of reasons for refusal, outgoing documents such as decisions of refusal, amendments, and written opinions) of patents in Japan.
User registration is required to use this API, and there is a limit to the amount of access because it is a trial version.
Japan Patent Office
https://www.jpo.go.jp/system/laws/sesaku/data/api-provision.html