• author: Nick Chapsas

Understanding API Versioning

APIs, or Application Programming Interfaces, are becoming increasingly important for modern software. They allow different applications to communicate with each other in a predefined, structured way. However, implementing an API comes with its own challenges, one of which is versioning.

In this article, we will discuss the importance of API versioning, why it is critical to maintain backwards compatibility, and show how to version an API in .NET Core.

What is API Versioning?

When you expose your API to the public or other consumers, everything that you expose is a contract that cannot be broken. An API version is essentially a contract that represents the features, endpoints, and functionality that is available in a specific version of an API.

The goal of versioning is to preserve backwards compatibility, which ensures that existing applications and clients that rely on an API will continue to function correctly.

Why is Versioning Important?

Breaking changes to an API can be disastrous for both the provider and consumer of the API. The provider risks losing consumer trust and potentially damaging its reputation, while the consumer can face unexpected downtime and increased development costs necessary to update to the new API version.

By introducing versioning, an API provider ensures that consumers can continue to depend on the contracts exposed by previous versions of the API without fear of unexpected changes.

Implementing Versioning in .NET Core

In .NET Core, we can implement versioning to our APIs with a few simple steps.

Step 1: Define API version

Typically, API versions start with a prefix such as v1/, v2/, etc. in the endpoint URL. This can be represented using a constant string in a separate Version class.


Step 2: Separate API Controllers by Version

Organize API versions by making separate controllers for each version, containing the same endpoints as the previous version. Separate these controllers into "subfolders" using an attribute that represents the version.

[ApiController][Route("api/{version:apiVersion}/users")][ApiVersion("1.0")]publicclassUsersController:ControllerBase{[HttpGet]publicIActionResultGet(){// return users}}

Step 3: Define API Version Route Templates

Define API version route templates in a separate class, which also includes the version.


Step 4: Implement API Route Templates

Finally, use the API version route templates in your controller method.

[HttpGet(ApiRoutes.V1.Users.GetAll)]publicIActionResultGet(){// return users}

By following these steps, we now have a versioned API that is backwards compatible and maintainable.


API versioning ensures that existing consumers of an API can continue to function correctly when new features are added or removed. As a result, API versioning is a critical part of API development that should be a top consideration for any API provider.

By versioning your APIs properly, you will ensure a smooth transition for consumers when new versions are released, avoiding dreaded breaking changes, and ensuring that the API remains future-proof.

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