What Is an API and How Does It Work: REST vs. GraphQL Explained in Simple Terms

Almost every digital product you use today, from a weather app and online banking to the online store where you shop, relies on an API in the background. When you pay by card on a website, when a courier service sends you an SMS with shipment status, or when your store automatically pulls prices from an ERP system, two completely different pieces of software are “talking” to each other. That conversation happens through an API.

The term is mentioned often, but it is rarely explained clearly to someone who is not a developer. Understanding the basics – what an API is, how it works, and how REST differs from GraphQL – is no longer just a technical detail. It directly affects how fast, scalable, and ready for future integrations your online store or application will be.

In short: an API (Application Programming Interface) is a set of rules that allows two software systems to exchange data and functionality without needing to know how the other system is built internally. REST and GraphQL are the two most common approaches to building APIs: REST separates data across individual addresses, or endpoints, and is currently the standard for around 93% of APIs in use, while GraphQL works through a single address and allows the client to define exactly which data it wants, making it a popular choice for more complex applications.

In the rest of this article, we explain:

• what an API is and how it works in practice
• which types of APIs exist
• what REST architecture is and what its principles are
• what GraphQL is and which problem it solves
• a direct comparison of REST and GraphQL, including a table
• when each approach is used in ecommerce and application development
• a concrete real-world example – Shopify’s API strategy shift

What Is an API?

An API (Application Programming Interface) is a programming interface that defines how two applications can communicate: which data they can request from each other, in which format and in what way.

Why are APIs needed at all?

• They allow different systems to exchange data without manual entry, for example, a store and an ERP system.
• They allow the same functionality to be used across multiple platforms: a website, mobile app, or external partners.
• They shorten development time because developers do not have to build every function from scratch. For example, you do not need to build your own card-processing system; you can use a ready-made API from a bank or payment provider.
• They enable process automation, such as stock synchronization, shipment tracking, and invoice sending.

The average application today communicates with dozens of external services through APIs, from payment and analytics systems to email services and data storage. In that sense, APIs are the connective tissue of modern software.

How Does an API Actually Work?

API communication comes down to two repeated steps: a request and a response.

• The client sends a request. This can be a mobile app, website, or another piece of software asking for a specific piece of information or action, for example, “send me the product list” or “create a new order”.
• The server processes the request. The server checks whether the request is valid, whether the client has permission for the requested action, and then retrieves or changes data in the database.
• The server returns a response. The response arrives in a standardized format, most often JSON (JavaScript Object Notation), together with a status code that shows whether the request was successful.

HTTP Methods – the “Verbs” of API Communication

Most APIs on the web communicate through the HTTP protocol, the same one your browser uses to load websites. Each request uses one of the standard HTTP methods:

Status Codes – Did the Request Succeed?

Every response carries a three-digit status code that immediately shows what happened:

• 200 OK – the request was processed successfully
• 201 Created – a new resource was created successfully
• 400 Bad Request – the request was not formed correctly
• 401 Unauthorized – authentication is missing or incorrect
• 404 Not Found – the requested resource does not exist
• 500 Internal Server Error – an error occurred on the server side

Authentication – Who Is Allowed to Use the API?

APIs are rarely completely open. To let the server know who is sending a request and whether they have permission, authentication mechanisms are used:

• API key – a unique code that identifies the application calling the API
• OAuth 2.0 – a standard that allows a user to sign in through a third-party service, for example “Sign in with Google”, without sharing a password
• Token-based authentication (JWT) – the server issues a temporary token after login, which is sent with every later request

The Most Common Types of APIs

The term “API” covers several different architectures and approaches. Here is an overview of the most important ones:

According to Postman’s State of the API report for 2025, which included more than 5,700 developers, architects and managers worldwide, REST still dominates by a wide margin: 93% of respondents use it. GraphQL is used by 33%, webhooks by 50%, and WebSocket by 35% of respondents. It is important to note that the survey allowed multiple answers, so the percentages show how many developers use a given approach at all, not which one is their only approach. In practice, REST and GraphQL are usually not mutually exclusive; they complement each other.

In the rest of the article, we focus on REST and GraphQL because they are the two competing approaches for designing the main API of your store or application, while Webhook, WebSocket, and SOAP solve other, narrower problems such as notifications, real-time communication, and legacy systems. As a rule, they are used alongside REST or GraphQL, not instead of them.

What Is a REST API?

REST (Representational State Transfer) is not a technology, but an architectural style for API design defined by Roy Fielding in his doctoral dissertation in 2000. A REST API organizes data as resources and assigns each resource its own address, or endpoint.

Basic principles of REST architecture:

• Resources have their own address. For example: /products, /products/128, /users/45/orders
• Stateless communication. The server does not remember previous requests; each request must contain all the data needed to process it.
• Standard HTTP methods. GET, POST, PUT, and DELETE have clearly defined meanings.
• Uniform interface. The response format is predictable and consistent, most often JSON.
• Suitable for caching. Responses to GET requests can be cached, which speeds up the application and reduces server load.

Example of a REST request for product information with ID 128:

GET /api/products/128

The server returns all data about that product: name, price, description, available quantities and images, even if the application currently needs only the price. This is REST’s biggest limitation: over-fetching, when more data is retrieved than needed, and under-fetching, when multiple different endpoints need to be called to display one page.

What Is GraphQL?

GraphQL is a query language and runtime for APIs developed by Facebook in 2012 and released as open source in 2015. Unlike REST, GraphQL does not have dozens of different addresses. The entire API is called through a single endpoint, and the client specifies within the query exactly which fields and related data it wants to receive.

Example of a GraphQL query for the same scenario, product ID 128, but only the name and price:

graphql

{

product(id: 128) {

name

price

}

}

The server returns exactly those two fields: nothing more, nothing less. If the frontend team later wants to display the product image as well, it simply adds image to the query, without the backend team needing to change the API or create a new endpoint.

Key advantages of GraphQL:

• No over-fetching or under-fetching – the client receives exactly what it asks for.
• One request instead of several. Product data, reviews, and recommended items can arrive in one query instead of three separate REST calls.
• Self-documenting schema. A GraphQL API comes with a built-in description of all available data, making frontend teams’ work easier.
• Flexibility for mobile applications, especially useful when the network is slow or limited because less data is transferred.

Limitations of GraphQL:

• It is harder to cache responses at the HTTP infrastructure level, such as a CDN or proxy, because most queries are sent as POST requests.
• More complex queries can burden the server if they are not properly limited.
• It requires a larger initial investment in knowledge and tools compared with a simple REST endpoint.

REST vs GraphQL – Direct Comparison

Note: usage data comes from Postman’s State of the API report for 2025 and refers to developers who use a given approach, with multiple answers allowed, not to API market share.

When to Use REST and When to Use GraphQL

There is no universally “better” solution; the choice depends on the specific project.

REST is the better choice when:

• You are building a public API that many external partners will use. REST is more familiar and easier to integrate.
• You need simple response caching for speed and lower server load.
• You are working with simple, well-defined resources, for example standard CRUD logic: create, read, update, and delete.
• The team already knows REST and the project has a limited deadline.

GraphQL is the better choice when:

• The frontend application, especially a mobile one, needs to display data from several different sources on one screen.
• Different clients, such as web, mobile app, or external partner, need different amounts of data from the same API.
• The team often changes and expands the interface, so it is useful for the frontend not to wait for backend changes.
• The application works under limited bandwidth conditions, such as mobile networks, where it is important to transfer as little data as possible.

In practice, many companies use both approaches in parallel: REST for simple public integrations, and GraphQL for their own frontend and mobile applications that require flexibility.

A Practical Ecommerce Example: Shopify’s Move to GraphQL

A good example of why the choice between REST and GraphQL is not only theoretical is Shopify. Shopify marked the REST Admin API as legacy on 1 October 2024, and from 1 April 2025 all new public apps must be built exclusively through the GraphQL Admin API. Endpoints related to products and variants stopped receiving new functionality, and development teams around the world had to migrate their integrations.

The reason is practical: GraphQL allows a product, its variants, stock, and prices to be retrieved in a single call, instead of sending a separate REST request for each of those pieces of data. For a store with thousands of items, this directly affects synchronization speed and server load.

This change is a good reminder of why it matters for your online store’s API architecture to be built professionally and kept up to date: an outdated integration can stop working overnight when a platform changes its rules. If you are considering Shopify store development or already have a store on this platform, changes like these directly affect how data synchronization and integration with other systems are handled.

Why APIs Are Critical for Your Online Store or Application

For business owners, an API is not an abstract technical term. It is the mechanism that allows your online store or application to work not in isolation, but as part of a wider business system. When we work on online store development, API integrations are part of almost every project:

• Integration with an ERP system – an API allows prices, stock, and product data to be automatically synchronized between the ERP system and the store, without manual entry.
• Card payment integration – payment systems such as CyberSource securely process transactions through APIs, without the store directly “seeing” card data.
• Courier service integration – an API enables automatic pickup requests, real-time status tracking and customer notifications.
• Integration with order management systems – orders can automatically move between the store, warehouse and external order processing software.

Without APIs, all these operations would require manual work: entering data, checking status, and updating prices, which significantly slows down operations and increases the risk of errors. If you are planning web application development that needs to communicate with other systems, such as a bank, ERP, CRM tool, or external service, choosing the right API architecture from the start saves time and money in the long run.

API Security – What to Pay Attention To

An API that is not properly protected is one of the most common entry points for attacks on websites and stores. A few basic rules:

• Never send API keys in frontend code that is visible to every website visitor.
• Use HTTPS for all communication; unencrypted data in transit can be intercepted.
• Limit the number of requests, or use rate limiting, to prevent abuse and server overload.
• Regularly rotate tokens and keys, especially after team changes or suspected compromise.
• Validate every input on the server side. Never trust data that comes from the client.

If you are interested in the broader picture of website and store protection, we wrote about it in more detail in the article How to protect yourself from hackers – basic security measures.

FAQ – Frequently Asked Questions About APIs

What Does API Stand For?

API stands for Application Programming Interface. It is a set of rules through which two software systems exchange data and functions.

Is GraphQL Better Than REST?

It is not universally better. It is better for specific scenarios, such as complex frontends and mobile applications that require flexible data retrieval. REST remains a better choice for simple public integrations and systems where easy caching matters.

Is an API the Same as an Integration?

Not exactly. An API defines the communication rules that one system exposes. Integration is the process of connecting two systems through those APIs. A developer uses the API to build a concrete connection between, for example, a store and an ERP system.

Does a Small Online Store Need to Think About APIs?

Yes. Even the smallest store uses APIs for card payment processing, sending order confirmation emails or connecting to a courier service. Understanding the basics helps you ask the right questions to the agency or developer working on your project.

Can REST and GraphQL Be Used Together in the Same Project?

Yes, and this is common practice. Some parts of the system, for example, integration with a payment provider, can remain on REST, while the part that directly affects the frontend or mobile app uses GraphQL for faster and more precise data retrieval.

Which Ecommerce Platforms Use REST and Which Use GraphQL?

Most platforms today offer both approaches. Shopify, for example, has moved to GraphQL as the primary API for new apps, while Magento (Adobe Commerce) and WooCommerce support both REST and GraphQL APIs, depending on the integration needs.

Do I Need a Developer to Use an API, or Are There No-Code Solutions?

For basic integrations, such as connecting a form to an email tool, there are no-code tools like Zapier or Make that use APIs in the background. For more complex, business-critical integrations, such as ERP, payments, and logistics, it is recommended to hire an experienced developer or agency.

Conclusion

An API is not just a technical detail handled “in the background”. It is infrastructure that determines how quickly, securely, and flexibly your online store or application can grow. REST remains a reliable, proven standard for most integrations, while GraphQL is increasingly taking the lead in projects where flexibility and fast data retrieval are priorities, as Shopify’s example clearly shows.

The right decision is rarely REST or GraphQL. In practice, it is usually REST and GraphQL, depending on which part of the system you want to solve.

If you are planning an online store or web application and are not sure which API architecture fits your project, we will be happy to help you make the right decision based on your specific needs. Contact us and let’s talk about your project.