From the Revit API Docs website:
Web-based, searchbable, and extensible Revit API documentation.
For more information about the API visit the Autodesk Developer Network.
Revit API Docs is brought to you by Gui Talarico. It’s free.
Revit API versions 2018, 2017, 2016, and 2015 are supported.
There’s more information available on the Revit API Docs website.
