PubMed API

Programmatic access to the 39+ million biomedical literature citations in the NCBI's PubMed database via the Entrez Programming Utilities (E-utilities).

The PubMed API is officially the NCBI's Entrez Programming Utilities (E-utilities): a suite of eight server-side programs for the Entrez database system. It uses a fixed URL syntax to execute search, link, and retrieval operations against PubMed and 38 other NCBI databases (e.g., Gene, Protein). Developers typically use ESearch to retrieve a list of unique identifiers (PMIDs) from the 39+ million citations, then use EFetch to download full records, often in XML format. Usage requires specifying `tool` and `email` parameters; limit your requests to three per second.

https://www.ncbi.nlm.nih.gov/books/NBK25501/