An API, short for application programming interface, is a connection between computers or between programs. It is a set of rules and calls that lets one piece of software use a service of another, and it is not used directly by a person. A document that describes these rules is also called an API specification.
History of API
Creator: No single creator. Maurice Wilkes and David Wheeler are credited with the first API specification. Year: 1968.
The idea of an API is older than the term. In the 1940s, Maurice Wilkes and David Wheeler built a software library for EDSAC. EDSAC was an early computer at Cambridge. Its subroutines were kept on punched paper tape. A filing cabinet held a library catalog of notes about each subroutine and how to use it. Today that catalog would be called an API specification.
Wilkes and Wheeler published their methods in a book. The book is The Preparation of Programs for an Electronic Digital Computer. It holds the first published API specification. Joshua Bloch later said that they latently invented the API, because the idea is discovered more than invented.
The phrase application program interface appears in a 1968 paper. The paper was presented at an AFIPS conference. Its title is Data structures and techniques for remote computer graphics. The authors used the term for the link between a graphics program and the computer. Fortran subroutine calls were meant to free programmers from the details of each display device. C. J. Date brought the term to databases in 1974.
Roy Fielding described Representational State Transfer (REST) in his 2000 doctoral dissertation. He wrote it at the University of California, Irvine. Web APIs then moved away from Simple Object Access Protocol (SOAP) services. They moved toward REST-style resources with HyperText Transfer Protocol (HTTP) methods. A web API defines the requests. It also defines the reply structure. Replies often use JavaScript Object Notation (JSON) or Extensible Markup Language (XML).
Changelog and latest update
The API idea has no single version history. Its main standards are in separate documents. The Internet Engineering Task Force (IETF) published RFC 9110, HTTP Semantics, in June 2022. It sets the meaning of HTTP methods, status codes and headers. Most web APIs use these rules. The document obsoletes nine earlier Request for Comments (RFC) documents. Among them are RFC 7233 on range requests and RFC 2818 on HTTP over Transport Layer Security (TLS).
The OpenAPI Initiative maintains the OpenAPI Specification. It describes HTTP APIs in JSON or YAML, a text format for data. Version 3.0.3 and version 3.1.0 came before it. One file can drive documentation, client code and tests. The specification site links to each earlier version.
The OpenAPI specification site links to earlier versions, such as 3.0.2, 3.0.3 and 3.1.0. Readers can compare the versions to see which fields changed.
Latest update: OpenAPI Specification 3.2.1, 2026-09-10
The OpenAPI Specification 3.2.1 is dated 10 September 2026. The spec.openapis.org page calls it the latest published version. The editor's draft is kept on GitHub. The specification describes paths, operations, parameters and responses. Software can read the whole description from one document.
Usage examples
An API call sends a request to a URL. It then reads a reply. A web API uses an HTTP method. GET reads data. POST creates data. The status code in the reply says what happened. For example, 200 means success and 201 means created. The four examples show a command-line request. They show a POST request from JavaScript and a request from PHP. They also show an OpenAPI description of one path.
R=octocat/Hello-World
curl -s https://api.github.com/repos/$RThe curl command sends a GET request to the GitHub REST API. The s option hides the progress meter. The reply is a JSON object that holds the full name of the repository, its owner and its settings. The request needs no access token for public repositories.
const u = "https://httpbin.org/post";
const res = await fetch(u, {
method: "POST",
headers: {
"Content-Type": "application/json"
},
body: JSON.stringify({ title: "Hi" })
});
console.log(res.status);The fetch call sends a POST request with a JSON body to a public test address. The Content-Type header tells the server that the body is JSON. The httpbin service echoes the posted JSON and replies with status 200. The console line prints that status code.
<?php
$u = "https://httpbin.org/json";
$ch = curl_init($u);
curl_setopt($ch,
CURLOPT_RETURNTRANSFER, 1);
$body = curl_exec($ch);
curl_close($ch);
$j = json_decode($body, true);
echo $j["slideshow"]["title"];
?>The curl_init function opens a connection to the URL. CURLOPT_RETURNTRANSFER returns the reply as a string. The json_decode function turns the JSON text into a PHP array. The last line prints the slideshow title.
openapi: 3.2.1
info:
title: Shop API
version: 1.0.0
paths:
/orders/{id}:
get:
summary: Get one order
responses:
"200":
description: The orderThe openapi line sets the specification version. The info block names the API and its version. The paths block declares a GET operation for one order. The id value in braces is a path parameter. The 200 response describes the reply the server sends.
References
These sources are outside Websnoogie and were checked on 2026-10-12.
API
Wikipedia
The encyclopedia article on the API concept. It traces the term from the 1940s EDSAC library to the 1968 graphics paper. It defines an API specification. It covers web APIs that use HTTP, JSON and XML.
API | MDN Web Docs Glossary
MDN Web Docs (Mozilla)
The MDN glossary entry that defines an API. It explains browser APIs and server APIs. It links to reference pages for the Web APIs that browsers give to scripts.
Web APIs | MDN Web Docs
MDN Web Docs (Mozilla)
The MDN index of the Web APIs that browsers expose to JavaScript. Examples include fetch, the DOM and storage. Each entry lists its methods and browser support.
RFC 9110: HTTP Semantics
RFC Editor (IETF)
The IETF document from June 2022. It defines the meaning of HTTP methods, status codes and header fields. Most web APIs follow these rules. It states how a GET or POST request must be handled. It replaces the earlier HTTP semantics RFCs that its header lists.
OpenAPI Specification, latest version
OpenAPI Initiative
The OpenAPI Specification in its latest version, 3.2.1. It is dated 10 September 2026. It defines the fields of an API description for paths, operations, parameters and responses. It lists the required fields for each part of the description.
Connect your site to the tools you already use
Customers often ask us whether an API can link their website to another program. An API, which stands for application programming interface, is a set of rules that lets two programs exchange data. A booking tool, a payment service or a mailing list can send data to a site through one. Each link adds a new path, and a careless link can expose data. We tie every link to a clear purpose before we build it.
When we build a link through an API, we first confirm the keys, limits and fields the other program requires. We keep secret keys on the server, never in the page a visitor can view. We send one test record from start to finish, then check the result on a phone. Our hosting runs at 99.999% uptime, so the link stays available when visitors arrive.
Local search engine optimization (SEO) is $190 a month, and it works with the data your site shares. A bundle of a domain and WordPress hosting costs $24.99 for the domain and $149 for hosting. Call 402-813-4034, open from 7 am to 10 pm daily, and name the program you want to connect.
