An Introduction to Versioning APIs in ASP.NET

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In an API-first world, it’s more important than ever for developers to keep track of their APIs and prevent issues like breaking changes. This is where API versioning comes in: by providing a way to identify different versions of your API, you can avoid unexpected errors like 502 status codes.

ASP.NET 6 introduces a number of new features for building APIs. One of these features is API versioning, which enables you to specify different versions of your API and control how they are accessed.

This .NET programming tutorial discusses API Versioning, why it is needed, its types and a few code examples to illustrate the concepts covered.

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What Is API Versioning?

API versioning is a process that allows multiple versions of an API to be distributed and used by different clients. It helps to ensure that the APIs are stable, reliable, and compatible. API versioning can be used to provide backward compatibility with older versions of your API, or to enable customers to choose the version of the API they want to use.

API versioning is a software engineering practice that allows you to evolve your API over time in ways that can be managed and controlled. It also allows you to change your API without breaking existing clients, ensuring backward compatibility.

Developers can release new versions of your API without breaking existing clients by using the same interface as they do now, but with some new functionality added behind it. Programmers can leverage API Versioning to manage different versions of an API.

API Versioning allows developers to build newer features and improvements of an API while still supporting older versions. This ensures that users of your API can continue to use it without interruption, even as you make changes and updates.

What are the Benefits of API Versioning?

The key benefit of this approach is that when it comes time for upgrades, programmers do not have to force existing users to upgrade at the same time or even make them aware that an upgrade has happened at all.

Versioning is especially important if you are working with other developers on the same project because they need to know what version they are working with and how it compares to older versions of your API.

Here are a few points that discuss why you should version your APIs:

API Versioning Allows You to Control What Users See and Use

When you version your APIs, you can control which users see which versions of your APIs. This is important because you don’t want consumers of your APIs to be using outdated or unsupported features. By keeping track of which versions of your APIs are supported, you can ensure that all users have access to the latest features and improvements.

API Versioning Allows You to Manage Changes and Updates

One of the biggest benefits of versioning an API is that it allows you to manage changes and updates more effectively. By versioning your APIs, you can prevent incompatible changes from being made to the same parts of the API. This means that changes made to an API in one release won’t affect clients using older releases. This prevents problems from occurring and keeps the API stable and reliable.

API Versioning Helps You Avoid Compatibility Issues

API Versioning also helps avoid compatibility issues between different versions of an API. When two versions of an API are used together, they can clash and cause problems for users. By versioning your APIs, you can prevent these problems from happening and ensure that your users are always using the latest and most compatible version of your API.

API Versioning Helps You Improve Quality and Reliability

Versioning your APIs also helps improve the reliability and quality of your API. By tracking which versions of the API are being used, you can make sure that the code is always up to date and bug-free. This helps to ensure that your users have a positive experience when using your API and that they get the best possible results from it.

Looking for versioning systems and version control software? We have a great tutorial listing the Best Version Control Software to help get you started.

Best Practices in Versioning APIs

Below are some of the best practices developers and programmers should use when versioning APIs:

  • You should always use the latest version of the ASP.NET Core framework when developing your APIs. This will ensure that you have access to the latest features and that your APIs are as performant as possible.
  • Take advantage of Semantic Versioning to version your APIs. This will make it easy for clients to determine which API version they need to use and will help avoid any compatibility issues.
  • You must ensure to test your API updates in a staging environment before the software is released to the public. This will help ensure that there are no unexpected compatibility issues with existing clients.

When using semantic versioning for your APIs, you can follow the Major.Minor.Patch convention. Here, Major refers to a major change or incompatible API changes, Minor refers to a version used to maintain backward compatibility, and Patch denotes a version that contains the bug fixes.

Implementing API Versioning in ASP.NET 6

This section discusses the various ways in which you can implement API Versioning in ASP.NET 6.

Versioning with URL Routing

URL routing lets you specify which URL should be used to access a particular version of your API. For example, if you have an API that versioned using URL routing, you could specify the following route config file:


If you wanted to change the version of your API, all you would have to do is update the route parameter. This makes versioning your API quick and easy.

Versioning using HTTP Header

API versions can be specified using the “X-API-Version” HTTP Header. This header can be included in any response that represents a version of the API. The format for specifying an API version using the “X-API-Version” HTTP Header is:

HTTP/1.1 200 OK
Content-Type: application/vnd.api+json; charset=utf-8
X-API-Version: 1.0

If a client requests an API that doesn’t have the specified “X-API-Version” header, then the server will return a 404 Not Found error. In addition, if a new version of the API is released and includes changes that break existing clients, then servers should automatically update their APIs to include the new version’s “X-API-Version” header.

Servers should also notify clients of any changes in the version number using other means such as email or notifications on developer portals.

Versioning using the Query Parameter

For example, if you have an API that returns a list of products, you can specify which version of the API your client should use by including the query parameter “version”. For example, if you have an API that returns the list of products for the current month, you would include the query parameter “version=1”.

Keeping your API up-to-date ensures that your clients always have the latest version especially when your API is updated. If your clients are using an older version of your API, they may not be able to take advantage of new features or functionality that has been added to newer versions of your API.

By using the query parameter “version”, developers can ensure that your clients always use the most up-to-date version of your API.

Final Thoughts on API Versioning

API versioning is a process that allows multiple versions of an API to be distributed and used by different clients. It helps to ensure that the APIs are stable, reliable, and compatible. By versioning your API, you can control the changes made to your API and ensure that your clients are using the correct version of the API. This also allows you to deprecate older versions of the API, which can help to keep your API up-to-date and ensure that your clients are using the latest version of an API.

Read more ASPNET programming tutorials and software development guides.

Joydip Kanjilal
Joydip Kanjilal
A Microsoft Most Valuable Professional in ASP.NET, Speaker, and Author of several books and articles. More than 25 years of experience in IT with more than 18 years in Microsoft .NET and its related technologies. He was selected as a Community Credit Winner at several times. He has authored 8 books and more than 500 articles in some of the most reputed sites worldwide including MSDN, Info World, CodeMag, Tech Beacon, Tech Target, Developer, CodeGuru, and more.

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