There is some info in JSON:API — Recommendations which I can’t tell if you’ve looked at.
When determining an API’s URL structure, it is helpful to consider that all of its resources exist in a single “reference document” in which each resource is addressable at a unique path. Resources are grouped by type at the top level of this document. Individual resources are keyed by ID within these typed collections. Attributes and links within individual resources are uniquely addressable according to the resource object structure described above.
This concept of a reference document is used to determine appropriate URLs for resources as well as their relationships. It is important to understand that this reference document differs slightly in structure from documents used to transport resources due to different goals and constraints. For instance, collections in the reference document are represented as sets because members must be addressable by ID, while collections are represented as arrays in transport documents because order is significant.
URLs for Resource Collections
It is recommended that the URL for a collection of resources be formed from the resource type.
For example, a collection of resources of type photos will have the URL:
URLs for Individual Resources
Treat collections of resources as sets keyed by resource ID. The URL for an individual resource can be formed by appending the resource’s ID to the collection URL.
For example, a photo with an ID of “1” will have the URL:
Relationship URLs and Related Resource URLs
As described in the base specification, there are two URLs that can be exposed for each relationship:
the “relationship URL” - a URL for the relationship itself, which is identified with the self key in a relationship’s links object. This URL allows the client to directly manipulate the relationship. For example, it would allow a client to remove an author from a post without deleting the people resource itself.
the “related resource URL” - a URL for the related resource(s), which is identified with the related key within a relationship’s links object. When fetched, it returns the related resource object(s) as the response’s primary data.
It is recommended that a relationship URL be formed by appending /relationships/ and the name of the relationship to the resource’s URL.
For example, a photo’s comments relationship will have the URL:
And a photo’s photographer relationship will have the URL:
It is recommended that a related resource URL be formed by appending the name of the relationship to the resource’s URL.
For example, the URL for a photo’s comments will be:
And the URL for a photo’s photographer will be:
Because these URLs represent resources in relationships, they should not be used as self links for the resources themselves. Instead the recommendations for individual resource URLs should still apply when forming self links.