RetroContext is a web-based search tool for historians in the arts and humanities. It performs a full-text content search in various digital libraries by using their local search interfaces. Results are combined into one integrated list and can be filtered by metadata. The purpose of this tool is to discover historical documents in which the searched item is mentioned.
This tool is a prototypical implementation with Google Books API as a demonstrator for sources and Published Date as a demonstrator for metadata filters. A public beta release is planned for early 2017.