I only recently started using the ASP.NET Core's minimal API style, but an annoying thing I already encountered is the "long parameter list" problem. Route handlers that accept five, six, or seven parameters start to feel unwieldy fast. The good news is that a solution exists through the [AsParameters] attribute, introduced in .NET 7, that gives you a clean way out.
The problem it solves
Minimal APIs are appealing precisely because they're lightweight — no controllers, no ceremony. But that simplicity starts to break down as your endpoints grow more complex. Consider this example endpoint:
That's eight(!) parameters before you've written a single line of business logic. It's hard to read, hard to test, and grows more painful every time requirements change.
Enter [AsParameters]
[AsParameters] lets you group related parameters into a plain C# class or record and bind them all at once. ASP.NET Core inspects the type's constructor and public properties to figure out where each value comes from — route, query string, header, or body — using the same binding rules it always has.
Here's the same endpoint rewritten:
And the parameter object:
The handler signature is immediately easier to scan. The parameter object is independently readable, testable, and reusable across multiple endpoints if needed.
How binding works
[AsParameters] doesn't change the binding rules — it just applies them to the members of your type instead of to the handler's parameter list directly. Each property or constructor parameter is bound according to the usual conventions:
- Route values bind by name matching a route template segment (e.g.,
{id}) - Query string is the default fallback for simple types
[FromHeader],[FromRoute],[FromQuery],[FromBody]attributes work exactly as they do on regular parameters
This means you can mix binding sources freely within a single parameter object:
Remark: Records with positional constructors are a natural fit because they're concise and immutable by default. But classes with settable properties work too, and give you more control when you need to mix binding attributes.
A real-world example
Putting it all together — a paginated, filtered product listing endpoint:
Notice that you can use multiple [AsParameters]-decorated parameters on the same handler — a great way to separate concerns like filtering, pagination, and sorting into distinct reusable types.
Wrapping up
[AsParameters] is a small attribute with a meaningful quality-of-life impact. It doesn't fundamentally change how binding works in minimal APIs — it just lets you organize your parameters into proper types instead of cramming everything into the handler signature.
The full binding attribute toolkit ([FromRoute], [FromQuery], [FromHeader], [FromBody]) works seamlessly inside your parameter objects, so you're not giving anything up.
For any endpoint that's grown beyond three or four parameters, it's worth reaching for.
More information
AsParametersAttribute Class (Microsoft.AspNetCore.Http) | Microsoft Learn
Parameter binding in Minimal API applications | Microsoft Learn