A method and system for sharing full text index entries across application boundaries in which documents are obtained by a shared, platform level indexing service, and a determination is made as to whether the received documents are duplicates with regard to previously indexed documents. If a document is determined to be a duplicate, the index representation of the previously indexed copy of the document is modified to indicate that the document is also associated with another application or context. If a document is not a duplicate of a previously indexed document, the document is indexed to support future searches and/or other processing. The index representation of a document includes application category identifiers associating one or more applications or contexts with the document. When a document is indexed, one or more category identifiers are generated and stored in association with that document. The category identifiers for an indexed document may, for example, represent an application that received, stored, or otherwise processed that document. The application category identifiers enable category specific searching by applications sharing a common search index. A software category filter may be provided to process search results from the shared search index, so that only documents associated with certain categories are returned. Accordingly, one or more search categories may be determined for a given search query, based on an application generating the search query, or some other context information, and then used to filter the search results provided from the shared search index.