API

in English: application programming interface

basicwidespread

An API is a predefined rule set that allows one program to request data or a service from another without needing to know its internal workings.

In plain terms

Imagine a restaurant: you do not go into the kitchen, but order from the menu through the waiter, who brings out what you asked for. An API is the same in the world of programs: the menu says what can be requested and how, and the waiter passes on the request and brings back the response. The kitchen, meaning the inside of the other program, stays hidden.

It is useful so that software does not have to build everything itself. An online store does not write its own banking system but calls the payment provider's API; a weather application does not operate measuring stations but retrieves data from the meteorological service.

It matters twice over for artificial intelligence. First, companies mostly build large language models into their own products via APIs. Second, an AI agent also acts through APIs: that is how it books appointments, sends emails or queries a database.

It differs from a website or an application screen in that it is not designed for humans. It contains no buttons or images, only precisely formatted requests and responses that another program reads.

How it works

In a typical web API, the provider publishes a description: what requests its system accepts, in what format, and what response it returns.
The calling program identifies itself, usually with a secret API key or access token, which functions like an entry card.
It sends the request to a specified web address, for example, "provide tomorrow's forecast for Budapest".
The provider verifies authorization and whether the caller has exceeded their limits, then executes the task.
The response returns in a machine-readable, standardized format (most often JSON), which the calling program then processes and displays to you.

An everyday example

When you pay by bank card in an online store, the shop's page communicates with the payment provider via an API, which then confirms whether the charge was successful. Similarly, an API brings the map into the food-ordering app, and the web-based customer service chat, powered by a language model, receives its response through an API.

Who is affected

everyoneAlmost every application you use daily retrieves data via APIs in the background, from maps to payments.

developerMost modern software is built by connecting APIs of ready-made services, and AI models can be integrated in the same way. → Code

entrepreneur, executiveThe available APIs determine how easily your company's billing system, online store, and CRM can be connected, while the price of AI services typically depends on the volume of usage via the API.

bank customer, investorOpen banking is built on APIs: with your consent, an external application can thus access your account data or initiate payments on your behalf. → Money

A common misconception

MythAn API is a separate program or application that can be downloaded and installed.

In realityAn API is not a standalone product but a regulated entry point to an existing system: an agreement on what can be requested from it and how. On its own, it does nothing; the work is done by the system behind it.

Limits and risks

It creates dependence on the provider: if they change, raise the price, or shut down their API, the application built on it may stall.
An API key is like a password: if it leaks, others can use the service in your name and at your expense.
Most APIs have usage limits and fees; for AI models, you typically pay per processed text volume, which can add up quickly.
If an agent can act via APIs, it can also make mistakes with them, so it is advisable to precisely define what access it has.

Similar, but not the same

User interface – The user interface with buttons and screens serves the human, while the API makes the same system available to programs.
Model Context Protocol (MCP) – MCP is an open standard enabling AI agents to access diverse tools and data sources in a unified way; it does not replace APIs, as APIs often underlie the tools.
SDK (Software Development Kit) – An SDK is a package of ready-made code that facilitates the use of an API, but is not the gateway itself.

Related concepts

Broader

Software infrastructure, Interface, System Integration

Narrower

REST API, Webhook, API key, Modell-API

On the edge

Model Context Protocol (MCP), Tool use, Cloud service, SDK, Token

A brief history

The term first appeared in print in 1968 in a study on computer graphics by Ira W. Cotton and Frank S. Greatorex. The most widespread web style today, REST, was described by Roy Fielding in his 2000 doctoral dissertation.

Where things stand

The API has been the basic tool for connecting software for decades, and by the end of 2026 it has also become one of the main channels for business use of AI models. What is new is that APIs are increasingly called not by a pre-written program but by an autonomously working agent.

Status: 2026 November

In the news

Appears in 32 Agent Age stories; the curve shows weekly occurrence in the news magazine.

GitHub Copilot impact dashboard adds chat and VS Code agent usage, code review gets API controlsNov 6, 2026 · Code
Meta makes advertisers solely responsible for its AI changes to ads; new API features arriveNov 2, 2026 · Marketing
Anthropic adds message threads to its API, but the token bill stays the sameNov 2, 2026 · Code
Anthropic watermarks four older Claude models under EU AI Act; xAI to enable Grok API text watermarkingOct 31, 2026 · Agent Age
Bank AI projects: OpenAI on COBOL migration, Danske Bank API agents, BNK group-wide platformOct 21, 2026 · Money
Veryfi launches AI suite to screen checks, invoices and receipts for document fraudOct 21, 2026 · Money
China approves overseas use of DeepSeek and MiniMax models as DeepSeek open-sources its inference engineOct 19, 2026 · Agent Age
Hackers hit OpenCode AI coding tool, running up charges on users' AI accountsOct 19, 2026 · Code

Also known as

API · API-k · Application programming interface · application programming interface · Programming interface · application programming interface · webes API · web API

Sources

This entry was machine-edited and has undergone machine expert review; the “In the news” section updates automatically from Agent Age stories.