Hypertext Transfer Protocol (HTTP) and modern HTTPS (S for Secure) requests have three parts: the required request line, and the optional body and headers. Every request has a certain method—the most popular are GET and POST. The specific usage of different methods can vary for specific API endpoints. Most web APIs have parameters defined within their URLs.

HTTP responses have a similar structure, but also a universal HTTP status code, representing the request status. The most frequently used codes are 200 (success), 403 (forbidden, bad authentication), and 404 (URL not found). You can read more on different status codes at Mozilla's MDN website (https://developer.mozilla.org/en-US/docs/Web/HTTP/Status).

With this general understanding of APIs and HTTP requests, let's take a look at a particular geocoding service—Nominatim.