New API Keys for the E-utilities
If you regularly use the E-utilities API you might want to read this.
After May 1, 2018, NCBI will limit your access to the E-utilities unless you have one of these keys. Obtaining an API key is quick, and simple, and will allow you to access NCBI data faster. If you don’t have an API key, E-utilities will still work, but you may be limited to fewer requests than allowed with an API key.
After May 1, 2018, any computer (IP address) that submits more than 3 E-utility requests per second will receive an error message. This limit applies to any combination of requests to EInfo, ESearch, ESummary, EFetch, ELink, EPost, ESpell, and EGquery.
If you write software of scripts that access the E-utilities API then the users will need to get their own api key. Calls will have this format