Searching DOI metadata
Both Datacite and Crossref have simple REST-like search endpoints.
Datacite Search
The DataCite search is at http://search.datacite.org.
The DataCite search API is at api is based on SOLR and can be found at http://api.datacite.org/
An example search that returns JSON
Crossref search
The crossref search is at http://search.crossref.org. The CrossRef search API can be found at http://api.crossref.org
An example search that returns JSON
External documentation
Datacite search API documentation
Crossref search API documentation
Updated less than a minute ago