The Force.com REST API lets you integrate with Force.com applications using simple HTTP methods, in either XML or JSON formats, making this an ideal API for developing mobile applications or external clients. Force.com also supports Apex REST, which lets you create Web services on Force.com using Apex.
Consider the following benefits of using the REST API in your integrations:
This page is the primary resource page for the REST API.
To begin learning about the REST API, follow this path.
Here are some other helpful resources for the Force.com REST API.
Workbench (Tool that provides a REST API Explorer)