Before data is transmitted over the internet, it is compressed using a widely used technique called GZip. Its primary goal is straightforward: reduce the size of web replies to speed up loading times.

Today, a vast quantity of text-based data, including HTML, JSON, CSS, JavaScript, XML, and more, is sent by web apps. All of this information is sent across the network each time a user accesses a webpage or API. Your program will immediately become slower and feel heavier if these files are huge.

This issue is resolved by GZip compression, which shrinks the answer before it leaves the server.

1. Faster Applications Through Smaller Responses

Most content sent from a server is text, and text compresses extremely well. With GZip, responses can shrink by 60–90%, often even more.

For example:

2. Lower Bandwidth and Hosting Costs
Every byte you send costs something, especially in cloud environments.

When responses are compressed:

• Servers send less data
• Cloud bandwidth usage drops
• API traffic becomes cheaper
• Users save mobile data
• Applications scale better with lower load

For high-traffic APIs, this becomes a huge cost-saving advantage.

3. Better SEO and Web Performance
Google cares deeply about speed. Faster websites rank better and deliver better Core Web Vitals, such as:

• LCP (Largest Contentful Paint)
• FCP (First Contentful Paint)
• Overall loading experience

GZip improves these metrics automatically because it reduces how much content must be downloaded.

In .NET Core, GZip Works Automatically When Hosted on IIS
When a .NET Core application runs behind IIS or IIS Express, you automatically get GZip compression without writing any code. This is because IIS applies compression through its built-in StaticCompressionModule and DynamicCompressionModule, which run before the request reaches your .NET Core application.

So:

• You do not need to add AddResponseCompression()
• You do not need to configure any middleware
• IIS provides GZip automatically for all .NET apps, including .NET Core and .NET 6/7/8
• Visual Studio also uses IIS Express → so compression appears automatically during development

GZip seems like a .NET Core feature, but it is actually IIS doing the work, not the .NET runtime.

GZip is one of the easiest and most impactful optimizations you can use in .NET applications—and understanding how IIS and .NET handle it helps ensure your application performs consistently across all environments.