The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →An API (Application Programming Interface) is a defined set of rules that lets one piece of software request data or functionality from another. For example, a weather app can ask a weather service for a forecast; the app sends a request, the service returns data, and the app displays it.
What is an API?
An API is an interface—a set of features and rules—that allows software to interact with other software or hardware. Think of it as a contract: the provider specifies what a program can ask for, how to ask, and what kind of result to expect. The API does not necessarily expose everything the provider can do; its owner decides which functions and resources are available.
APIs are not limited to websites. Operating systems and software libraries have APIs, and browsers provide APIs that let web pages use browser or device capabilities.
How does a web API work?
A typical web API exchange involves a client and a server. The client is the software making a request; the server provides a resource or service and returns a response. A mobile app, for example, can act as a client even though no person is directly using a web page.
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- The client has a task. A weather app needs current forecast information for a location.
- It sends a request. The app directs the request to an API endpoint—the address or software location that receives it—and formats the request according to the API’s rules.
- The service processes it. The weather provider checks the request and determines what information the client is permitted to receive.
- The server returns a response. The app receives the result and presents the forecast to the user.
For example, an API might accept a request containing an employee’s name and a date range, then return the number of hours worked during that period. The exact request fields and response contents depend on that API’s schema, which describes acceptable request formats and response structures. Some APIs also require authentication or specific permissions.
What are endpoints and schemas?
Endpoint
An endpoint is the particular address or location to which a client sends an API request, or where a request is handled. An API may offer multiple endpoints for different resources or actions. It is a software address, not a physical object.
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Schema
A schema documents the shape and rules of API messages: what a request may or must contain, and what the response can look like. Following the schema helps a client and server interpret the same request and result consistently.
APIs you may already use
Weather apps and remote services
A weather app can request forecast data from a weather provider’s software and display the returned conditions. This is a web API example: one application communicates with a service over a network.
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A timesheet service can receive an employee name and a date range, then return hours worked. This illustrates that an API can provide a service or perform a task, not just return a simple file or web page.
Browser and device capabilities
Browser APIs let code use features of the browser or connected device. The Geolocation API can provide available location information, while getUserMedia can request access to a webcam or microphone. Browser APIs can also let a page update its content through the DOM or fetch data to update part of a page without reloading the whole document.
API, HTTP, REST, and SOAP: what is the difference?
These terms describe different parts of software communication; they are not synonyms. An API is the interface and rules. HTTP is a protocol often used to carry web API requests and responses. REST is an architectural style, while SOAP is a protocol.
| Term | What it describes | How it relates to an API |
|---|---|---|
| API | An interface and rules for software interaction | Defines what a client can request and how the provider responds |
| HTTP | A client/server messaging and resource-transfer protocol | Often carries web API requests and responses |
| REST | An architectural style for distributed systems | A way to design distributed interfaces; an HTTP API is not automatically RESTful just because it uses HTTP |
| SOAP | A communication protocol | Can be used to build SOAP APIs |
RPC and WebSocket are other approaches used for software communication. RPC centers on calling a procedure remotely; WebSocket supports two-way communication over a connection. These describe different patterns from REST and SOAP, and no approach is universally best—the fit depends on the system’s needs.
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Browser APIs, third-party APIs, libraries, and frameworks
These categories can overlap in a project, but they refer to different things.
- Browser API: An interface provided by the browser environment, such as Geolocation,
getUserMedia, or the DOM. - Third-party API: An interface offered by an external platform or service for other software to use, such as a weather service’s forecast API.
- Library: Reusable code whose methods a developer calls. A library may itself expose an API.
- Framework: A structure that calls a developer’s code at defined points as part of the framework’s flow. A framework can also expose APIs.
So, using a library or framework is not the same as using an API, although those tools commonly provide APIs of their own. Likewise, a browser API is an API, but it does not have to contact a remote website.
Quick Recap
What to remember when using an API
- Identify the endpoint and the API’s accepted request format before sending a request.
- Check the schema to understand the response your code should handle.
- Expect access controls: an API provider may require authentication or limit which data and functions a client can use.
- Keep the categories straight: HTTP is a protocol, REST is an architectural style, and SOAP is a protocol—not alternative names for an API.
Sources and further reading
- MDN Web Docs: Introduction to client-side APIs
- AWS AppSync Developer Guide: What is an API?
- Cloudflare: What is an API?
- MDN Web Docs: An overview of HTTP
- MDN Web Docs: REST
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