Swagger will show the individual endpoints and the search parameters that can be used, but it doesn’t do a great job of documenting what the response types will be.
The best document that shows in terms of data response fields of what we support in OpenEMR is the 4.0.1 specification for FHIR US Core Profiles (version 3.1.0 of US Core) that we certified ONC against: HL7.FHIR.US.CORE\Home - FHIR v4.0.1
Looking at the Differential Table for each profile will show what OpenEMR absolutely supports in terms of fields returned. For example this is the Allergy Intolerance profile and if you look at the Differential Table it shows the mandatory fields we support.
This can be derived programatically through the metadata endpoint in OpenEMR and hitting the profile definitions off of HL7:
As a broad overview, we support all of the mandatory read and search requirements that are outlined in US Core for those FHIR endpoints. There are a lot more optional fields supported by the FHIR resources but we’ve implemented very few of those.
There are a couple of create/update FHIR resources I think for patient and Practitioner but when I started looking at them we were not really spec compliant on them.
I’m in the middle of a project that will implement in a module the FHIR Questionnaire and QuestionnaireResponse endpoints and a very rudimentary version of the Task FHIR resource but that’s where things stand right now.