scholarly-metadata
Crossref REST API
The authoritative registry of DOI metadata for scholarly publishing, covering roughly 165 million records. Look up any DOI to retrieve its bibliographic record, or search by title and author, on the website or through a free open API. It is the backbone reference for verifying citations and finding out what a DOI actually identifies.
Academic papers API
Why it’s useful & how it works
Spine of the science wave. No key; add ?mailto= for the polite pool. DOI->metadata is tiny JSON, works both ways.
What’s inside
~165M+ DOIs.
API access
https://api.crossref.org/works/ <doi> ; query ?query=...&mailto=<email>
Access
Programmatic API access (a key may be required — see the API tag).