# API

Category: [Agents & Protocols](https://seo-geo-glossary.com/en/glossary/category/agents-protocols/) › [Agent protocols](https://seo-geo-glossary.com/en/glossary/category/agents-protocols/agent-protocols/) · Also known as: application programming interface

An **API** (application programming interface) is, in MDN's wording, a set of features and rules in a software program that lets other software interact with it, as opposed to a human user interface. In SEO work, the term usually refers to web APIs that a service exposes over HTTP.

## How does an API work?

In web development an API consists of methods, properties, events or URLs that developers can use. The calling software sends a request that follows the API's rules. The API replies in an agreed format, often JSON. AWS and IBM both describe this as a client and server exchange of requests and responses.

MDN separates browser APIs from the wider group of web APIs. Browser APIs give access to browser and device features, such as the Geolocation API. Third-party web APIs expose the data or functions of an external service. IBM lists REST as the dominant style for web APIs, alongside SOAP, GraphQL and RPC variants.

## Example

A request to a fictional API, for illustration:

```http
GET /api/pages/42 HTTP/1.1
Host: example.com
Accept: application/json
```

A possible response:

```json
{ "id": 42, "title": "Home", "status": 200 }
```

## Why do APIs matter for SEO and AI?

Analytics and SEO platforms expose their data through APIs, so reports can feed dashboards, business intelligence tools or data warehouses. AI agents call APIs through tool calling. An OpenAPI description makes an API easier to understand for people and programs, and MCP servers can make APIs available to AI applications.

## FAQ

**What does API stand for?**
Application programming interface.

**What is an example of an API?**
IBM names the "Pay with PayPal" button, where an API connects a shop to the payment processor behind the scenes.

**What is the difference between an API and a web API?**
An API can belong to any software, including an operating system. A web API is reached through web protocols such as HTTP.

## At a glance

- **Type:** interface through which software interacts with other software
- **Used in:** web APIs over HTTP, browser APIs in the browser
- **Response format:** often JSON
- **Docs:** [MDN: API](https://developer.mozilla.org/en-US/docs/Glossary/API)

Last checked: October 8, 2026

*Diagram: How MCP connects applications and tools.* According to the MCP specification, a host starts one client per server. Servers offer tools, resources and prompts and run locally (stdio) or remotely (Streamable HTTP). WebMCP is a draft by a W3C community group, not a W3C standard. Here the web page provides its tools inside the browser.

## Related terms

- [OpenAPI](https://seo-geo-glossary.com/en/glossary/openapi/index.md)
- [MCP server](https://seo-geo-glossary.com/en/glossary/mcp-server/index.md)
- [Tool calling](https://seo-geo-glossary.com/en/glossary/tool-calling/index.md)
- [Search Console API](https://seo-geo-glossary.com/en/glossary/search-console-api/index.md)
- [Google Indexing API](https://seo-geo-glossary.com/en/glossary/google-indexing-api/index.md)
- [History API](https://seo-geo-glossary.com/en/glossary/history-api/index.md)

## Sources

- [API – MDN Web Docs Glossary](https://developer.mozilla.org/en-US/docs/Glossary/API)
- [What is an API? – AWS (secondary)](https://aws.amazon.com/what-is/api/)
- [What is an API? – IBM (secondary)](https://www.ibm.com/think/topics/api)

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Last updated: October 8, 2026
URL: https://seo-geo-glossary.com/en/glossary/api/