13. A system of one or more computers configured to perform operations comprising: providing, to a client device, information for presenting a search engine user interface for a third party content provider; receiving, from the client device, a search query entered using the search engine user interface; processing the search query to determine a context identifier for a context file; retrieving a context file from the third party content provider identified by the context identifier; modifying the search query using one or more commands to produce a context processed search query, wherein the one or more commands are contained in the context file; providing the context processed search query to a search engine; obtaining, from the search engine, context processed search results responsive to the context processed search query; and providing the context processed search results to the client device.
13. A system of one or more computers configured to perform operations comprising: providing, to a client device, information for presenting a search engine user interface for a third party content provider; receiving, from the client device, a search query entered using the search engine user interface; processing the search query to determine a context identifier for a context file; retrieving a context file from the third party content provider identified by the context identifier; modifying the search query using one or more commands to produce a context processed search query, wherein the one or more commands are contained in the context file; providing the context processed search query to a search engine; obtaining, from the search engine, context processed search results responsive to the context processed search query; and providing the context processed search results to the client device. 17. The system of claim 13 , wherein the commands comprise a command that reformulates the search query.