Additionally, you mentioned descriptions and keywords. These would not be provided directly by the opensearch api so you might be thinking of using the generator version of it (action=query&generator=prefixsearch) to get the results augmented (ex: /w/api.php?action=query&format=json&prop=extracts&generator=prefixsearch&exlimit=5&exintro=1&explaintext=1&gpssearch=yah&gpslimit=5). I'm not personally sure how expensive that is, someone else would have to chime in.