The W3C DDR Simple API provides read-only functionality to allow an adapting application to provide Evidence, in the form of HTTP headers, that identifies the Delivery Context and allows it to query the DDR for values of properties of the Delivery Context identified. In addition, it provides access to basic catalog information that allows an application to find out which properties are supported.

The need for Device Descriptions (information about the Properties of various Aspects of the Delivery Context) is not confined to the mobile Delivery Context. It is common practice for Web sites to detect the type of user agent ("browser sniffing") to determine possibly small but important differences between various desktop Web browsers and adapt content to accommodate those differences.