1. A method, comprising: determining, by one or more data processing apparatus and for a prefix that represents a portion of a search query, one or more completions that yield a completed search query when combined with the prefix; identifying one or more content items for the one or more completions; receiving, through a search engine input field presented at a user device, user input including the prefix; identifying, by one or more data processing apparatus and based on the user input, the one or more content items for the one or more completions; determining, based at least in part on display specifications of the user device, a visual format for a given content item from the one or more identified content items, wherein a first visual format presents a Uniform Resource Locator (URL) on a same line as other information in the given content item, and a second visual format presents the URL on a different line than the other information; and providing, by one or more data processing apparatus and prior to a completed search query being specified by the user input, the given content item with instructions that cause the given content item to be presented according to the determined visual format and at a display location corresponding to the one or more completions for which the given content item was identified.