So what is an API? An API, short for application programming interface, allows different software programmes to communicate with each other. It lets one programme request information or ask another programme to complete a task without needing to know how that programme works behind the scenes.
Think of it like ordering food at a restaurant. You tell the waiter what you want, the waiter gives your order to the kitchen and brings your food back when it's ready. You don't need to know how the kitchen prepares your meal. You just need to know what's on the menu and how to order it.
An API works in a similar way. One programme sends a request, the API passes it to another system and a response comes back. According to MDN Web Docs, APIs provide a set of rules that software programmes follow when communicating with each other.
The important thing is that each programme only shares the information or functions it's designed to make available. One system doesn't need access to everything happening inside another system to get the information it needs.
For example, when you use a weather app, it doesn't need to run its own weather stations. It can request weather information from another company's API and display the results on your screen.
How APIs work: A request goes out, a response comes back
Most APIs work through a simple process. One programme sends a request to another, and the second programme sends back a response. For example, say your business has a website that displays current weather conditions for customers planning outdoor activities.
When someone visits the page, your website sends a request to a weather service's API. The weather service looks up the conditions for that location and sends the information back. Your website then displays the temperature, wind speed and other details.
This usually happens in seconds, without the visitor knowing that two different systems are communicating.
There are three important things to understand about this process.
- The programmes don't have to be built the same way. Your website and the weather service might use completely different programming languages and systems. The API allows them to exchange information anyway.
- Requests need to follow specific rules. The API expects information in a certain format. If a request is missing information or uses the wrong format, the system may return an error instead of the requested data.
- Responses use a structured format. Many web APIs send information using JSON (JavaScript Object Notation). This is a way of organising data so software can easily identify details such as names, prices or temperatures.
Many APIs use HTTP, the same communication protocol web browsers use to load websites. You can learn more about how this works in freeCodeCamp's guide to APIs. Each request is processed, and the system sends back a response. If the programme needs more information, it can send another request.
API examples you already rely on
You probably use APIs every day without realising it. They're behind many of the features we expect websites and apps to have.
Here are four common examples.
- Payment processing: When someone buys something from your website, an API can connect your checkout system to a payment provider. The payment service processes the transaction and sends back a response telling your website whether the payment was approved or declined. This allows your business to accept payments without building its own payment processing system. The provider can also handle payment details securely, so your website doesn't need to receive or store raw card information.
- Maps and locations: Businesses can use mapping APIs to display maps, calculate distances and provide directions. For example, a delivery company could use an API to calculate the distance between two postcodes or show customers where their deliveries are.
- Sign-in services: When you see a "Sign in with Google" option on a website, APIs help the website communicate with Google's sign-in service. Google verifies the user's identity and sends back information the website can use to sign them in. The website doesn't need access to the person's Google password.
- Data exchange: APIs let business software share information automatically. For example, your online shop could send sales information to your accounting software, or your marketing platform could pull new customer details from your customer relationship management (CRM) system.
In each example, the API allows one programme to use information or services provided by another. Your business gets the features it needs without having to build everything from scratch.
The building blocks: Requests, endpoints and authentication
You don't need to understand programming to get the basic idea of how APIs work. There are three terms worth knowing: requests, endpoints and authentication.
Requests
A request is the message one programme sends to another asking for information or an action. For example, your website might send a request to an inventory system asking how many units of a product are available. It could also request customer information, create a new order or update an existing record.
Each request needs to follow the API's rules so the receiving programme knows what to do. Think of it like filling out an online form. If the form asks for your name, email address and order number, you need to provide that information in the expected fields. An API request works in a similar way.
Endpoints
An endpoint is a specific address where a programme sends an API request. One API might have several endpoints, each designed to handle a different task. For example, an online shop's API could have one endpoint for product information, another for customer records and another for processing refunds.
When software needs product information, it sends the request to the product endpoint. If it needs to create a refund, it uses the refund endpoint. The API's documentation explains which endpoints are available, what each one does and how requests should be formatted.
Authentication
Authentication is how an API checks that a programme or user is allowed to access it. Many APIs require an API key, which is a unique code that identifies the application making the request. Think of it like a membership card. When the programme sends a request, it includes the key so the API can identify who's asking.
Other APIs use authentication tokens. These are credentials that can provide access for a limited time or grant permission to perform specific tasks without sharing a user's password.
Authentication helps prevent unauthorised access, but systems may also need separate permission checks to decide what an authenticated user or programme is allowed to do. IBM's API authentication documentation explains some of the ways APIs verify requests.
How APIs make software integration possible
One of the biggest benefits of APIs is that they allow different business programmes to work together. This is called software integration.
Without integration, employees may need to manually move information between systems. For example, someone might have to copy customer details from an online shop into accounting software, then enter the same information into a delivery system.
APIs can help automate those steps. Here's an example of how it might work for an online retailer.
- A customer places an order on your website.
- Your website sends the order details to your inventory system through an API.
- The inventory system updates the available stock.
- Your shipping software uses a courier's API to arrange delivery.
- The courier sends back a tracking number.
- Your website uses that information to send the customer a shipping confirmation.
Instead of an employee entering the same information into several systems, the programmes exchange the details automatically. APIs make this possible by providing a consistent way for each programme to send and receive information.
Of course, connecting systems isn't always as simple as switching on a setting. Someone may still need to configure the integration, match information between programmes and decide what should happen if something goes wrong.
However, once the connection is working, APIs can eliminate a lot of repetitive administrative work.
Permissions, reliability, documentation and security: What to know
APIs can make business software much more useful, but there are a few things to consider before relying on them.
Permissions control access
An API shouldn't automatically give every connected programme access to everything in your system. Instead, permissions determine what each application can see or change.
For example, your accounting software might need permission to read order information from your online shop. That doesn't mean it should also be able to delete customer accounts or change product listings.
When setting up an integration, check what permissions the connected software requests and limit access to what it actually needs.
Reliability matters
When your business uses an API, you're depending on another system to be available and working correctly. If that service has an outage, your integration may stop working until the problem is fixed.
Changes to an API can also cause problems. For example, if a provider changes how requests need to be formatted, software using the old format may start receiving errors.
Before choosing a service, check whether the provider publishes information about outages, scheduled maintenance and upcoming API changes. For important processes, it's also worth setting up alerts or automatic retries when requests fail.
Documentation explains how everything works
API documentation is essentially the instruction manual for connecting to a service. It explains what the API can do, which endpoints are available, what information requests need to include and how the system responds.
Good documentation also explains error messages, authentication requirements and any restrictions on how often you can send requests.
If you're evaluating software because of its API capabilities, take a look at the documentation before committing. Even if you won't be setting up the integration yourself, your developer or IT team will need clear instructions to get everything working.
Security needs more than a password
APIs can handle sensitive information, including customer details, financial records and business data. That makes security especially important.
Along with authentication and permissions, look for these protections.
- Encryption: APIs should use secure connections, such as HTTPS, to protect information as it travels between systems.
- Rate limiting: This restricts how many requests an application can send within a certain period, helping prevent abuse and excessive traffic.
- Secure API keys: Keys and authentication tokens should be stored securely instead of being shared publicly or included in exposed code.
- Access monitoring: Logs and alerts can help identify unusual activity or unauthorised requests.
Postman's API security guide explains why using several security measures together is important.
Keep in mind that integrations also need maintenance. If you're connecting software to save just a few minutes of work each month, the cost and effort of maintaining that connection may outweigh the benefits.
When does connecting systems through an API make sense?
APIs are especially helpful when your business uses several programmes that need to share information regularly.
Here are four situations where an API connection may be worth considering.
- You're entering the same information into multiple systems. If employees regularly copy orders, customer details or other information between programmes, an API could automate that work and reduce mistakes.
- You need up-to-date information in different places. APIs can help keep inventory counts, customer records, delivery information and other data current across multiple systems. For example, when someone buys the last item in your online shop, an API can update the stock level in your inventory system.
- You need a feature your software doesn't have. Instead of building your own payment processing system, mapping service or messaging platform, you can connect to an existing provider through its API.
- You repeat the same tasks across different programmes. If employees follow the same steps every day or week, an API integration may allow those tasks to happen automatically.
Before setting up an integration, identify the task you're trying to make easier. Then check whether your existing software has an API that supports it.
Not every API gives you access to every feature in a programme. For example, software might let employees create reports through its dashboard but not offer an API endpoint for generating those reports automatically.
It's also important to check whether API access is included in your subscription. Some providers only offer it with more expensive plans or charge extra based on usage.
Start with one repetitive task that's taking up too much time. Test the connection, make sure the information is transferring correctly and see whether it actually saves your team time. Once that integration is working, you can look for other opportunities to connect your business tools.
The takeaway
APIs allow different software programmes to communicate, share information and complete tasks together. They're what make many everyday features possible, from processing online payments to displaying maps and keeping business records updated across different systems.
For businesses, APIs can reduce repetitive work, improve accuracy and make existing software more useful.
You don't need to understand how to build an API to benefit from one. Start by looking at the programmes your business already uses and identifying information that employees regularly move between them.
If those systems offer API connections, you may be able to automate some of that work and give your team more time to focus on other tasks.
Sources
- MDN Web Docs — API glossary definition
- MDN / Learn web development — Introduction to web APIs
- freeCodeCamp — "What is an API and How Does it Work? APIs for Beginners"
- Postman blog — "API Security Best Practices"
- IBM documentation — "Authenticating API requests"
