While there are a handful of community hosted sites for Revit API documentation, it always bugged me that the only ‘official’ source required opening the SDK as (1) no one had time for all that when trying to point people in the right direction and (2) it added another technical barrier to get started with the tool. My choice of past tense there as there is finally official API documentation in the Revit help documents starting with 2026.1.
This source doesn’t replicate the features of the community sites, as it does not aim to replace the immense value those provide. But by having it in the official help documentation we get some certainty that with each release and update of Revit we should always have a source for guiding others and finding what is available.