Useful API reference of the most frequently used types and objects implemented in .NET object model and at least one client programming model. .NET client-side object model (CSOM), JavaScript object model (JSOM), and/or REST.

CSOM JSOM and REST API index

CSOM JSOM and REST API index part 2

CSOM JSOM and REST API index part 3

CSOM JSOM and REST API index part 4

Ref: SharePoint 2013 .NET Server, CSOM, JSOM, and REST API index