A hardware and/or software facility facilitates search string entry and refinement on a mobile device. A user enters a search string on a mobile device via one or more input methods. The facility searches the user's device and/or one or more remote data areas and returns search results that match the entered search string. Search results include, for example, information, links, files, and other results that correspond to the search string. Before and/or after the search is performed, the facility applies one or more filters that produce refined search results. Filters may relate to location, category, synonyms, data type, social-network, and other groupings—including user-defined groupings—that may refine the search results. Filters may be applied automatically and/or in response to user selection of a filter.