Web service vs. API: A starter guide

It’s easy to get bogged down in technical terms if you’re talking about what goes on under the hood of a website or an app, but it’s also useful to know how the individual components of your tech stack communicate with each other.

In fact, understanding how communication and data exchange takes place helps developers make important decisions about software architecture — and craft better digital experiences. 

In this post, we’re going to talk about the differences between web services and application programming interfaces (APIs), and how they power the experiences that you create for your audiences. The terms web service and API are often used interchangeably but they’re not really the same — let’s find out why. 

What is a web service?

A web service is a type of software that enables different systems to communicate over the internet. 

Web services require a network, and use standardized protocols like Web Services Description Language (WSDL), Hypertext Transfer Protocol (HTTP) or Simple Object Access Protocol (SOAP). Commonly found in environments which require a consistent and reliable level of machine-to-machine communication, web services are favored by large enterprise organizations operating multiple systems, and by organizations with strict interfaces between systems, such as those found in legacy architecture. Web services also typically focus on a single functionality, so software systems may utilize multiple web services to do different things.

Since they’re heavily standardized, web services leave little room for flexibility in the communication they facilitate — which makes them better suited to predefined, repetitive tasks, such as those associated with enterprise resource planning (ERP), telecommunications, and government databases. However, that strict formatting can make web services more challenging to maintain and place a heavier burden on overall system performance. 

What is an API?

Application programming interfaces, like web services, facilitate communication between software systems. However, APIs are broader interfaces than web services and do not need a network to communicate.

Nonetheless, their similarity leads many people to frame web services as a subset of API. In fact, you could even say: All web services are APIs but not all APIs are web services. 

However, where web services are heavily standardized and inflexible, APIs are versatile, and can use a huge variety of communication protocols. As we mentioned, APIs don’t need to communicate over the internet (or over a network) and can facilitate communication between two separate applications within the same device. 

APIs function by exposing an application’s data to another application directly. A client application sends an API call — a request for specific data — to an API endpoint, which is held within an API server. They come in many architectural styles: representational state transfer (REST), GraphQL, WebSockets, and more — each being suited to a particular form of communication between software systems. 

APIs are designed to be flexible so as to connect systems that use different protocols, and fast, so as to be responsive. Those characteristics mean that they’re useful in a variety of contexts, from server-to-server communications to real-time updates for mobile apps and IoT-connected devices.

For an example of an API-first software architecture, look no further than the Contentful Digital Experience Platform (DXP), which offers a completely composable environment in which to build unique tech stacks. For example, developers could choose Contentful’s headless content management system (CMS) to power their website and mobile app, and then add Lokalise to handle text translations for overseas customers, Shopify to handle payments, Bynder to pull in images or other media assets for your products pages, and so on. 

In that composable ecosystem, each component relationship is facilitated seamlessly by an API — so there’s no risk of coding complications, and content can be reused endlessly across different digital channels. 

What’s the difference between web services and APIs?

We mentioned that it’s possible to classify web services as a type of API — but, more specifically, web services are a type that strictly structures their communication and data exchange processes. 

To use a food analogy, you could think of web services as fast food delivery companies. You could, for example, order a “regular cheeseburger meal” from one of these companies, using a predefined, structured menu. You know exactly what you’re going to get, and what it will taste like, but you don’t have much scope to change the meal that will eventually be delivered.

APIs, on the other hand, offer more flexibility, and so they’re like making that same cheeseburger meal from a recipe at home — only now you have scope to customize. The recipe sets out the cooking instructions but you can choose your own bun, your own beef, and cheese, add seasoning, and so on. It takes a bit more work on your part, but you can create a meal more tailored to your tastes.

Swap “fast food” for “data exchange between software applications” and we start to see how web services and APIs fit into a tech stack. 

Web services vs. APIs: Side-by-side

When do you need a web service or an API?

There’s obviously a lot of API and web service crossover (they both use XML format data, for example), but, hopefully, we’ve set out the differences between the two approaches. With that in mind, let’s examine the specific applications of web services and APIs which might make you opt for one over the other. 

When to use web services

• Communication consistency: The standardized communication protocols of web services offer consistent, reliable communication between systems. If you’re connecting an ERP system to a customer data management (CDM) system in an enterprise organization, for example, a web service should be able to handle a sufficiently high volume of requests on a daily basis with consistency and reliability. Those factors extend to mobile applications. Certain apps, for example, require a high level of consistency to protect customers’ personal information. 

• Legacy solutions: Many legacy content management solutions are monolithic in the sense that they tightly couple their services across their front and back ends. In these environments, it’s difficult to make adjustments to individual parts of the tech stack without disrupting surrounding code, which makes it difficult to integrate new tools and functionalities to support or enhance workflows. 

With that in mind, the highly structured, standardized communication style of web services is better suited to monolithic systems because it’s less likely to integrate smoothly with other systems. 

When to use APIs 

• Quick deployment: Many companies need to develop and deploy new functionalities quickly, often working with software development kits (SDKs) that don’t necessarily facilitate communication with other systems. In these contexts, APIs allow developers to develop, prototype, and integrate additions to the tech stack quickly and facilitate the transfer of data between software systems smoothly.

• Omnichannel potential: APIs enable firms to pursue omnichannel strategies, which involve creating seamless content experiences across different digital channels. With APIs handling communication between the CMS and the various touchpoints, content teams can create content once, and then publish it on any channel, without risk of formatting or coding complications. 

• Reusable content: The API-first approach allows brands to reuse it in any part of their digital infrastructure, from web pages and apps, to emails, memos, and newsletters. Content can be created once, stored in a centralized location and retrieved for use quickly and easily. 

• Headless and composable scalability: Headless and composable software architectures are inherently modular and extensible, and so APIs enable developers to integrate new microservices in different programming languages, as needed, as they build out the tech stack. That extensibility means that APIs are ideal for brands that are seeking to scale their tech stacks. 

• Security: APIs offer robust security protections. As a first line of defense, users need to obtain an API key before they can access the API. Going further, API keys can be combined with secure, token-based authentication methods such as OAuth 2.0, as well as encrypted data transfer via HTTPS. These protections help control who can access the APIs, and what actions they’re authorized to perform — making APIs a strong choice for protecting sensitive data and ensuring regulatory compliance.

• Dynamic requests: APIs are capable of managing dynamic, real-time interactions between systems, pulling in data or services seamlessly to meet user needs. That makes them ideal for apps that require frequent updates, such as breaking news apps, taxi apps, and flight trackers, and so on. 

Build with Contentful

The choice between using web services or APIs is going to depend heavily on context — that is, the needs of your tech stack, your content strategy, and your business. However, as a growing brand, with evolving, diverse content needs, it’s going to make sense to at least explore an API-first approach as a way to build flexibility and interoperability into your tech stack from the ground up. 

The Contentful Digital Experience Platform (DXP) takes an API-first approach, opening up a fully composable digital ecosystem and a vast Marketplace of microservices. In that environment, developers have the resources to build the content experiences that best reflect their brand, and content teams are empowered to publish content seamlessly on websites, mobile apps, wearables, or any other audience touchpoint.

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