GZip is a popular compression technology used to reduce the size of data before it is sent over the internet.
Its main purpose is simple: make web responses smaller so they load faster.
Web applications today transfer a huge amount of text-based data—HTML, JSON, CSS, JavaScript, XML and more. Each time a user loads a webpage or API, all this data travels across the network. If these files are large, your application instantly becomes slower and feels heavier.
GZip compression fixes this problem by shrinking the response 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:
| Type | Original Size | After GZip |
|---|
| JSON API | 150 KB | 20 KB |
| HTML Page | 100 KB | 15 KB |
| CSS File | 50 KB | 7 KB |
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.