If you still believe that every Web API should contain a service layer, the time is to rethink that belief.

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Hi, I’m Zoran, I have more than 25 years of experience as a software developer, architect, team lead, and more. I have been programming in C# since its inception in the early 2000s. Since 2017 I have started publishing professional video courses at Pluralsight and Udemy and by this point, there are over 100 hours of the highest-quality videos you can watch on those platforms. On my YouTube channel, you can find shorter video forms focused on clarifying practical issues in coding, design, and architecture of .NET applications.❤️
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Zoran Horvat

Service layers are often unnecessarily added to Web APIs. A service layer is only justified when orchestrating changes across multiple independent mutable systems (like a database and payment gateway). Most Web APIs write to a single database and read from multiple sources, making a service layer pure overhead. The one-to-one relationship between endpoints and service methods creates boilerplate code for DTO mapping, error translation, and localization without providing architectural value. The decision is simple: if your API doesn't orchestrate multiple transactional boundaries, skip the service layer and implement logic directly in endpoints.

Stop Adding a Service Layer to Every Web API

Everything he describes his API doing are things that only a service layer should ever be doing. None of that work should be done in the API layer for a reason. There shouldn’t be any business logic there. It’s the controller.
He’s breaking the pattern just to do it and have content for a video

This immediately closes an opportunity to use alternative I/O channel, like CLI. Introducing command to remove a record? Refactor the module or duplicate the code.
I’ve seen dozens of these “simple solutions” that becomes unmanageable mess the very next day it’s live. Because requirement changes. Because, suddenly, we have to maintenance and manage the data layer. Because most of the apps are rarely about “call an API and forget”.
Once team believes it is - it opens a dark cave of hunting bugs for months, because of logic duplication, missing edge case handling, validations and unauthorised access.

Point is well taken, in a trivial scenario, don’t make it worse, that’s fair. I do work with Python and I find the class based structure in C# with interfaces etc. troubling. But, one overriding issue does keep coming back: testing. Without a service layer that has it’s dependencies injected how do you do testing easily? With a service you can mock the dependencies and then test the return. If all you have is a ‘heavy’ controller then testing that structure is more difficult? I’m curious on how the author approaches this?