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APIs vs. Web Service: What’s the Difference?

illustrated computer with a light bulb and data cloud on the left and blog title on the right.

Key takeaway: All web services are APIs, but all APIs are not web services.

We live in a digital age where almost everything is done through an API or Web Service. Have you ever wondered about the differences? Why should you care? This blog breaks down the differences between APIs and Web Services and explains why you might need one or the other for your business.  


Application Programming Interface (API):

APIs are a set of routines, data structures, and protocols that support building applications. You can find them in libraries or operating system services such as those offered by the language in your projects.  

Web Service 

Web Services are a way to provide machine-to-machine communication over the internet. W3C defines them as software systems designed for interoperability and connectivity among devices, people, or organizations across networks.  

APIs vs Web services and what is the difference

APIs vs. Web Services 

Key takeaway: All web services are APIs, but all APIs are not web services.  

Style of Communication 

  • APIs: takes in any style of communication  
  • Web Services: supports styles such as Simple Object Access Protocol (SOAP), Universal Description Discovery and Integration (UDDI), and Web Services Description Language (WSDL)  


  • APIs: Don’t need a network  
  • Web Services: Need a network for its operation   

Web Services 101: Three Things You Need to Know 

1) Web Services can be developed by one company, used by another, and hosted by a third company. 

2) Developers can write Web Services in various languages and still have them communicate with one another by exchanging data using web services. 

3) Web means HTTP protocol, and Service refers to request/response. Web Services are not tied to any operating system or programming language.  

APIs 101: Three Things You Need to Know   

1) APIs and industry standards make communication easier between different programs. They don’t indicate or restrict how you use the data. What you do with the information is in your control. 

2) APIs allow you to get data between two systems in real-time. This means that you don’t have to wait for the data from one system to be copied over to the other system. You can start using the data as soon as they are entered into the first system, saving time for your team. 

3) An API defines how data is stored and transmitted between systems. An API also means the operations required to process the data. 

With industry-standard APIs in place, it’s now easier for one organization to say, “we support HR-Open version x,” and other organizations will know precisely what that means by learning the industry-standard API definitions and documentation when it comes to data representations and operations.

HR Open Standards Consortium
HR Open Standards Consortium (Leslie on the right)

Future Integrations: How Can You Help?  

ADP works with two industry standards at ADP: HR Open Standard and LIMRA. We spoke to Leslie E., Senior Director of Application Development, and she shared with us her take on integrations for our Human Capital Management (HCM) products.  

Q: What’s the difference between using HR Open standard and LIMRA?  

Leslie: ADP participates in two industry standards to understand the future of application development. If you are looking for help with your HR integration from a full hire to retirement, then HR Open is a great option. If you are more interested in voluntary benefits, LIMRA would be your perfect choice.  

Q: What’s the future of using API standards?  

Leslie: Using API standards is critical in moving forward. Our job is to make sure that we’re doubling down on investing our time to make these standards usable. A great best practice is to work with partners on terminology and sample data, then go through the translation step.  

LeslieQ: What’s the future in application development?  

Leslie: Moving forward, I’d like to see us all use integration and standards instead of building custom layouts. But it’s only possible when we work together to design, enhance, and maintain standards, ensuring they are meaningful and effective in application integrations.  

As our world becomes increasingly more complex, the need for APIs will continue to grow. They will allow businesses to quickly and easily bring together various applications to share data while hiding the details of how those systems work. The industry standards set by API providers help ensure that both sides of the integration use the same structure or schema, making it easy to repeat the implementation with other partners.    

Q: Why should we care about industry standards? 

Leslie: Efficient communication comes from using industry standards. Industry standards allow us to define a system record, translating our languages and partners’ languages into one common language. In the end, we provide a better experience for our clients, improving accuracy and reducing errors. It’s a win-win!    

Q: What’s one piece of advice for developers interested in using APIs? 

Leslie: When sharing information, remind your teams to be highly content-conscious when transmitting and securing the data sets. We have a detailed security review checklist for our partners here at ADP. Make sure everything you are doing in data transmittal follows strict security guidelines!  

Final Thoughts 

Developers continue to find ways of combining the two services to build more fantastic applications. The web APIs vs. service debate is not one with a clear-cut answer, but the benefits for both sides are adding more possibilities to application development.  

Do you prefer using one over the other? Both APIs and Web Services serve as essential cores in the field and are especially useful in different projects. Remember, while APIs can be one or offline, Web Services require a network. The overlapping idea is that all web services are APIs, but not all APIs are web services. 

Interested in a career in Application Development?   

Learn more about what it’s like working for ADP here and our current openings

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