With correspSearch you may search within the metadata of diverse digital or printed scholarly editions of letters. The web service assembles and analyses files in the "Correspondence Metadata Interchange format“ (CMIF) that has been (and will further be) developed by the Special Interest Group Correspondence of the Text Encoding Initiative (TEI). Apart from a website, correspSearch provides also an API which allows for automatic requests to the web service (the aggregated data is available under a free license). Scholarly editions are encouraged to provide their indexes of letters in the CMIF for this web service.