Google announced the release of a new API on Wednesday, giving direct access to the search analytics data within Webmaster tools. This data was already available in the Webmaster Tools user portal, but has never been made available as an API for third party apps to use before now.
Using the Search Analytics API, you can review your average site rankings in search, see the impressions your site links are getting in search results, monitor the CTR (clickthrough-rate) of your rankings in search, and more. Details on what’s available in the Search Analytics Report (which the API pulls data from) is available in the Search Analytics Report Documentation, or you can find more details on the API specifically here.