Can a Minimal API project include the Microsoft.AspNetCore.App framework?

Minimal API projects are part of asp.net core webapi website and are an alternative to creating MVC controllers. typically you would use the .Web sdk. the project should be producing a console app that hosts a webapi site. as you are implementing a web server, they are server side only.

sample webapi with Minimal API project with only the openapi nuget package added.

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="9.0.3" />
    <PackageReference Include="Microsoft.Extensions.ApiDescription.Server" Version="9.0.4">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
  </ItemGroup>

</Project>

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddOpenApi();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
    app.MapGet("/", () => Results.Redirect("openapi/v1.json"));
}

app.UseHttpsRedirection();

var summaries = new[]
{
    "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
};

app.MapGet("/weatherforecast", () =>
{
    var forecast =  Enumerable.Range(1, 5).Select(index =>
        new WeatherForecast
        (
            DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            Random.Shared.Next(-20, 55),
            summaries[Random.Shared.Next(summaries.Length)]
        ))
        .ToArray();
    return forecast;
})
.WithName("GetWeatherForecast");

app.Run();

record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary)
{
    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
}

note: if you call from Blazor WASM you will need to implement CORS. If the Blazor app is auto, you can use the hosting server project as a proxy to the minimal webapi project. see the yarp:

https://github.com/dotnet/yarp

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddOpenApi();

var app = builder.Build();

// Configure the HTTP request pipeline.

if (app.Environment.IsDevelopment())

{

app.MapOpenApi();

app.MapGet("/", () => Results.Redirect("openapi/v1.json"));

}

app.UseHttpsRedirection();

var summaries = new[]

{

"Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"

};

app.MapGet("/weatherforecast", () =>

{

var forecast =  Enumerable.Range(1, 5).Select(index =>

    new WeatherForecast

    (

        DateOnly.FromDateTime(DateTime.Now.AddDays(index)),

        Random.Shared.Next(-20, 55),

        summaries[Random.Shared.Next(summaries.Length)]

    ))

    .ToArray();

return forecast;

})

.WithName("GetWeatherForecast");

app.Run();

record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary)

{

public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);

}