Entrez Eutils
NCBI E-utilities and PubMed APIs are free public services provided by the National Library of Medicine (NLM), a branch of the U.S. National Institutes of Health. There are no paid tiers or subscription plans. Access is differentiated by whether an API key is used, which affects rate limits.
Entrez Eutils is the machine-readable pricing-plan profile for PubMed on the APIs.io network, conforming to the API Commons Plans specification.
It defines 2 plans, with named plans including Anonymous / No API Key, Registered API Key.
Tagged areas include biomedical, life science, research, literature, and citations.
Plans
Free access without registration. Limited to 3 API requests per second from a single IP address. Suitable for light, ad-hoc use and evaluation.
Free access with an NCBI API key obtained through a free NCBI account. Raises the rate limit to 10 requests per second. Required for production applications and automated systems that need higher throughput. Higher rates available upon request for special use cases.