Minimal APIs at a glance

Application
- WebApplication
- WebApplicationBuilder
Request Handling
Authorization
CORS
OpenAPI
Advanced
- Building libraries for ASP.NET Core
- Differences with ASP.NET Core MVC

WebApplication

Creating an application

var app = WebApplication.Create(args);

app.MapGet("/", () => "Hello World");

app.Run();

This listens to port http://localhost:5000 and https://localhost:5001 by default.

Changing the port

var app = WebApplication.Create(args);

app.MapGet("/", () => "Hello World");

app.Run("http://localhost:3000");

Multiple ports

var app = WebApplication.Create(args);

app.Urls.Add("http://localhost:3000");
app.Urls.Add("http://localhost:4000");

app.MapGet("/", () => "Hello World");

app.Run();

Reading the port from environment

var app = WebApplication.Create(args);

var port = Environment.GetEnvironmentVariable("PORT") ?? "3000";

app.MapGet("/", () => "Hello World");

app.Run($"http://localhost:{port}");

Changing the ports via environment variables

You can set the ASPNETCORE_URLS environment variable to change the address:

ASPNETCORE_URLS=http://localhost:3000

This supports multiple urls:

ASPNETCORE_URLS=http://localhost:3000;https://localhost:5000

Listening on all interfaces

var app = WebApplication.Create(args);

app.Urls.Add("http://*:3000");

app.MapGet("/", () => "Hello World");

app.Run();

var app = WebApplication.Create(args);

app.Urls.Add("http://+:3000");

app.MapGet("/", () => "Hello World");

app.Run();

var app = WebApplication.Create(args);

app.Urls.Add("http://0.0.0.0:3000");

app.MapGet("/", () => "Hello World");

app.Run();

This syntax also works in the environment variables:

ASPNETCORE_URLS=http://*:3000;https://+:5000;http://0.0.0.0:5005

HTTPS with development certificate

var app = WebApplication.Create(args);

app.Urls.Add("https://localhost:3000");

app.MapGet("/", () => "Hello World");

app.Run();

HTTPS with custom certificate

Using appsettings.json

{
  "Kestrel" :{
    "Certificates": {
      "Default": {
        "Path": "cert.pem",
        "KeyPath": "key.pem"
      }
    }
  }
}

Configuration via code

var builder = WebApplication.CreateBuilder(args);

// Configure the cert and the key
builder.Configuration["Kestrel:Certificates:Default:Path"] = "cert.pem";
builder.Configuration["Kestrel:Certificates:Default:KeyPath"] = "key.pem";

var app = builder.Build();

app.Urls.Add("https://localhost:3000");

app.MapGet("/", () => "Hello World");

app.Run();

Using the certificate APIs

using System.Security.Cryptography.X509Certificates;

var builder = WebApplication.CreateBuilder(args);

builder.WebHost.ConfigureKestrel(options =>
{
    options.ConfigureHttpsDefaults(httpsOptions =>
    {
        var certPath = Path.Combine(builder.Environment.ContentRootPath, "cert.pem");
        var keyPath = Path.Combine(builder.Environment.ContentRootPath, "key.pem");

        httpsOptions.ServerCertificate = X509Certificate2.CreateFromPemFile(certPath, keyPath);
    });
});

var app = builder.Build();

app.Urls.Add("https://localhost:3000");

app.MapGet("/", () => "Hello World");

app.Run();

Reading the environment

var app = WebApplication.Create(args);

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/oops");
}

app.MapGet("/", () => "Hello World");
app.MapGet("/oops", () => "Oops! An error happened.");

app.Run();

Reading configuration

var app = WebApplication.Create(args);

Console.WriteLine($"The configuration value is {app.Configuration["key"]}");

app.Run();

Logging

var app = WebApplication.Create(args);

app.Logger.LogInformation("The application started");

app.Run();

WebApplicationBuilder

Changing the content root, application name and environment

var builder = WebApplication.CreateBuilder(new WebApplicationOptions
{
    ApplicationName = typeof(Program).Assembly.FullName,
    ContentRootPath = Directory.GetCurrentDirectory(),
    EnvironmentName = Environments.Staging
});

Console.WriteLine($"Application Name: {builder.Environment.ApplicationName}");
Console.WriteLine($"Environment Name: {builder.Environment.EnvironmentName}");
Console.WriteLine($"ContentRoot Path: {builder.Environment.ContentRootPath}");

var app = builder.Build();

Changing the content root, application name and environment

These may also be specified via the following environment variables:

ASPNETCORE_ENVIRONMENT
ASPNETCORE_CONTENTROOT
ASPNETCORE_APPLICATIONNAME

OR via command line arguments:

--applicationName
--environment
--contentRoot

Adding configuration providers

var builder = WebApplication.CreateBuilder(args);

builder.Configuration.AddIniFile("appsettings.ini");

var app = builder.Build();

Reading configuration

By default the WebApplicationBuilder reads configuration from:

appSettings.json
appSettings.{environment}.json
environment variables
The command line

var builder = WebApplication.CreateBuilder(args);

// Reads the ConnectionStrings section of configuration and looks for a sub key called Todos
var connectionString = builder.Configuration.GetConnectionString("Todos");

Console.WriteLine($"My connection string is {connectionString}");

var app = builder.Build();

Reading the environment

var builder = WebApplication.CreateBuilder(args);

if (builder.Environment.IsDevelopment())
{
    Console.WriteLine($"Running in development");
}

var app = builder.Build();

Adding logging providers

var builder = WebApplication.CreateBuilder(args);

// Configure JSON logging to the console
builder.Logging.AddJsonConsole();

var app = builder.Build();

Adding services

var builder = WebApplication.CreateBuilder(args);

// Add the memory cache services
builder.Services.AddMemoryCache();

// Add a custom scoped service
builder.Services.AddScoped<ITodoRepository, TodoRepository>();

var app = builder.Build();

Customizing the IHostBuilder

Existing extension methods on IHostBuilder can be accessed using the Host property.

var builder = WebApplication.CreateBuilder(args);

// Wait 30 seconds for graceful shutdown
builder.Host.ConfigureHostOptions(o => o.ShutdownTimeout = TimeSpan.FromSeconds(30));

var app = builder.Build();

Customizing the IWebHostBuilder

Existing extension methods on IWebHostBuilder can be accessed using the WebHost property.

var builder = WebApplication.CreateBuilder(args);

// Change the HTTP server implemenation to be HTTP.sys based
builder.WebHost.UseHttpSys();

var app = builder.Build();

Changing the web root

By default, the web root is relative to the content root in the wwwroot folder. This is where the static files middleware expects to find static files. You can change this by using the UseWebRoot method on the WebHost property:

var builder = WebApplication.CreateBuilder(args);

// Look for static files in webroot
builder.WebHost.UseWebRoot("webroot");

var app = builder.Build();

Custom dependency injection container

This example uses Autofac

var builder = WebApplication.CreateBuilder(args);

builder.Host.UseServiceProviderFactory(new AutofacServiceProviderFactory());

// Register your own things directly with Autofac here. Don't
// call builder.Populate(), that happens in AutofacServiceProviderFactory
// for you.
builder.Host.ConfigureContainer<ContainerBuilder>(builder => builder.RegisterModule(new MyApplicationModule()));

var app = builder.Build();

Adding Middleware

Any existing ASP.NET Core middleware can be configured on the WebApplication:

var app = WebApplication.Create(args);

// Setup the file server to serve static files
app.UseFileServer();

app.Run();

Developer Exception Page

The WebApplication has a the developer exception enabled by default when the environment is development:

var app = WebApplication.Create(args);

app.MapGet("/", () => throw new InvalidOperationException("Oops, the '/' route has thrown an exception."));

app.Run();

Navigating to / will render a friendly page that shows the exception.

ASP.NET Core Middleware

Middleware	Description	API
Authentication	Provides authentication support.	`app.UseAuthentication()`
Authorization	Provides authorization support.	`app.UseAuthorization()`
CORS	Configures Cross-Origin Resource Sharing.	`app.UseCors()`
Exception Handler	Globally handles exceptions thrown by the middleware pipeline.	`app.UseExceptionHandler()`
Forwarded Headers	Forwards proxied headers onto the current request.	`app.UseForwardedHeaders()`
HTTPS Redirection	Redirect all HTTP requests to HTTPS.	`app.UseHttpsRedirection()`
HTTP Strict Transport Security (HSTS)	Security enhancement middleware that adds a special response header.	`app.UseHsts()`
Request Logging	Provides support for logging HTTP requests and responses.	`app.UseHttpLogging()`
W3C Request Logging	Provides support for logging HTTP requests and responses in the W3C format.	`app.UseW3CLogging()`
Response Caching	Provides support for caching responses.	`app.UseResponseCaching()`
Response Compression	Provides support for compressing responses.	`app.UseResponseCompression()`
Session	Provides support for managing user sessions.	`app.UseSession()`
Static Files	Provides support for serving static files and directory browsing.	`app.UseStaticFiles()`, `app.UseFileServer()`
WebSockets	Enables the WebSockets protocol.	`app.UseWebSockets()`

Routing

You can route to handlers using the various Map* methods on WebApplication. There's a Map{HTTPMethod} method to allow handling different HTTP methods:

app.MapGet("/", () => "This is a GET");
app.MapPost("/", () => "This is a POST");
app.MapPut("/", () => "This is a PUT");
app.MapDelete("/", () => "This is a DELETE");

Other HTTP methods:

app.MapMethods("/options-or-head", new [] { "OPTIONS", "HEAD" }, () => "This is an options or head request ");

Route Handlers

Route handlers are methods that execute when the a route matches. Route handlers can be a function or any shape (including synchronous or asynchronous). It can be a lambda expression, a local function, an instance method or a static method.

Lambda expression

app.MapGet("/", () => "This is an inline lambda");

var handler = () => "This is a lambda variable";

app.MapGet("/", handler);

Local function

string LocalFunction() => "This is local function"

app.MapGet("/", LocalFunction);

Instance method

var handler = new HelloHandler();

app.MapGet("/", handler.Hello);

class HelloHandler
{
    public string Hello() 
    {
        return "Hello World";
    }
}

Static method

app.MapGet("/", HelloHandler.Hello);

class HelloHandler
{
    public static string Hello() 
    {
        return "Hello World";
    }
}

This provides the appropriate flexiblity when deciding how to organize your route handlers.

Naming routes and link generation

Routes can be given names in order to generate URLs to them. This avoids having to hard code paths in your application.

app.MapGet("/hello", () => "Hello there")
   .WithName("hi");

app.MapGet("/", (LinkGenerator linker) => $"The link to the hello route is {linker.GetPathByName("hi", values: null)}");

Route names are inferred from method names if specified:

string Hi() => "Hello there";

app.MapGet("/hello", Hi);

app.MapGet("/", (LinkGenerator linker) => $"The link to the hello route is {linker.GetPathByName("Hi", values: null)}");

NOTE: Route names are case sensitive!

These names must be globally unique and are also used as the OpenAPI operation id when OpenAPI support is enabled (see the OpenAPI/Swagger section for more details).

Route Parameters

You can capture route parameters as part of the route pattern definition:

app.MapGet("/users/{userId}/books/{bookId}", (int userId, int bookId) => $"The user id is {userId} and book id is {bookId}");

The route handler can declare the parameters that it wants to capture, and when a request is made to this route, the parameters will be parsed and passed to the handler. This makes it easy to capture the values in a type safe way (above, you can be sure that the userId and bookId are both int).

If the route values are not valid ints then an exception will be thrown. The following request will result in the exception below:

GET /users/hello/books/3

Microsoft.AspNetCore.Http.BadHttpRequestException: Failed to bind parameter "int userId" from "hello".
    at Microsoft.AspNetCore.Http.RequestDelegateFactory.Log.ParameterBindingFailed(HttpContext httpContext, String parameterTypeName, String parameterName, String sourceValue, Boolean shouldThrow)
    at lambda_method1(Closure , Object , HttpContext )
    at Microsoft.AspNetCore.Http.RequestDelegateFactory.<>c__DisplayClass37_0.<Create>b__0(HttpContext httpContext)

Wildcards/Catch all routes

app.MapGet("/posts/{*rest}", (string rest) => $"Routing to {rest}");

Route constraints

Route constraints are influence the matching behavior of a route.

app.MapGet("/todos/{id:int}", (int id) => db.Todos.Find(id));
app.MapGet("/todos/{text}", (string text) => db.Todos.Where(t => t.Text.Contains(text));
app.MapGet("/posts/{slug:regex(^[a-z0-9_-]+$)}", (string slug) => $"Post {slug}");

Path	Match
`/todos/1`	`/todos/{id:int}`
`/todos/something`	`/todos/{text}`
`/posts/mypost`	`/posts/{slug:regex(^[a-z0-9_-]+$)}`
`/posts/%`	No match

Contraints

constraint	Example	Example Matches	Notes
`int`	`{id:int}`	`123456789`, `-123456789`	Matches any integer
`bool`	`{active:bool}`	`true`, `FALSE`	Matches `true` or `false`. Case-insensitive
`datetime`	`{dob:datetime}`	`2016-12-31`, `2016-12-31 7:32pm`	Matches a valid `DateTime` value in the invariant culture. See preceding warning.
`decimal`	`{price:decimal}`	`49.99`, `-1,000.01`	Matches a valid `decimal` value in the invariant culture. See preceding warning.
`double`	`{weight:double}`	`1.234`, `-1,001.01e8`	Matches a valid `double` value in the invariant culture. See preceding warning.
`float`	`{weight:float}`	`1.234`, `-1,001.01e8`	Matches a valid `float` value in the invariant culture. See preceding warning.
`guid`	`{id:guid}`	`CD2C1638-1638-72D5-1638-DEADBEEF1638`	Matches a valid `Guid` value
`long`	`{ticks:long}`	`123456789`, `-123456789`	Matches a valid `long` value
`minlength(value)`	`{username:minlength(4)}`	`Rick`	String must be at least 4 characters
`maxlength(value)`	`{filename:maxlength(8)}`	`MyFile`	String must be no more than 8 characters
`length(length)`	`{filename:length(12)}`	`somefile.txt`	String must be exactly 12 characters long
`length(min,max)`	`{filename:length(8,16)}`	`somefile.txt`	String must be at least 8 and no more than 16 characters long
`min(value)`	`{age:min(18)}`	`19`	Integer value must be at least 18
`max(value)`	`{age:max(120)}`	`91`	Integer value must be no more than 120
`range(min,max)`	`{age:range(18,120)}`	`91`	Integer value must be at least 18 but no more than 120
`alpha`	`{name:alpha}`	`Rick`	String must consist of one or more alphabetical characters, `a`-`z` and case-insensitive.
`regex(expression)`	`{ssn:regex(^\\d{{3}}-\\d{{2}}-\\d{{4}}$)}`	`123-45-6789`	String must match the regular expression. See tips about defining a regular expression.
`required`	`{name:required}`	`Rick`	Used to enforce that a non-parameter value is present during URL generation

Parameter Binding

Parameter binding is the process of turning request data into strongly typed parameters that are expressed by route handlers. A binding source determines where parameters are bound from. Binding sources can be explict or inferred based HTTP method and parameter type.

Supported binding sources:

Route values
Query string
Header
Body (as JSON)
Services provided by dependency injection
Custom

NOTE: Binding from forms are not natively supported in this release.

GET, HEAD, OPTIONS, DELETE

The HTTP methods GET, HEAD, OPTIONS, DELETE will never bind from body. All other binding sources are supported.

NOTE: If you need to support the case where you have a GET with a body, you can directly read it from the HttpRequest.

var builder = WebApplication.CreateBuilder(args);

// Added as service
builder.AddSingleton<Service>();

var app = builder.Build();

app.MapGet("/{id}", (int id, int page, Service service) => { });

class Service { }

Parameter	Binding Source
id	route value
page	query string
service	provided by dependency injection

Other verbs (POST, PUT, PATCH, etc)

var builder = WebApplication.CreateBuilder(args);

// Added as service
builder.AddSingleton<Service>();

app.MapPost("/", (Person person, Service service) => { });

class Service { }

record Person(string Name, int Age);

Parameter	Binding Source
person	body (as JSON)
service	provided by dependency injection

Explicit Parameter Binding

Attributes can be used to explicitly declare where parameters should be bound from.

using Microsoft.AspNetCore.Mvc;

app.MapGet("/{id}", ([FromRoute] int id, 
                     [FromQuery(Name = "p")] int page, 
                     [FromServices] Service service, 
                     [FromHeader(Name = "Content-Type")] string contentType) => { });

Parameter	Binding Source
id	route value with the name id
page	query string with the name `"p"`
service	provided by dependency injection
contentType	header with the name `"Content-Type"`

Binding from form values is not supported at this time.

Optional parameters

Parameters declared in route handlers will be treated as required. This means if a request matches the route, the route handler will only execute if all required paramters are provided in the request. Failure to do so will result in an error.

app.MapGet("/products", (int pageNumber) => $"Requesting page {pageNumber}");

Since the pageNumber paramter is required, this route handler won't execute if the query string pageNumber isn't provided. To make it optional define the type as nullable.

app.MapGet("/products", (int? pageNumber) => $"Requesting page {pageNumber ?? 1}");

This also works with methods that have a default value:

string ListProducts(int pageNumber = 1) => $"Requesting page {pageNumber}";

app.MapGet("/products", ListProducts);

The above will default to 1 if the pageNumber isn't specified in the query string.

This logic applies to all sources.

app.MapPost("/products", (Product? product) => () => { });

The above will call the method with a null product if no request body was sent.

NOTE: If invalid data is provided and the parameter is nullable, the route handler will not be executed.

app.MapGet("/products", (int? pageNumber) => $"Requesting page {pageNumber ?? 1}");

The following request will result in a 400 (see the Binding Failures section below for more details)

GET /products?pageNumber=two

Special types

There are some special types that the framework supports binding without any explicit attributes:

HttpContext - The context which holds all the information about the current http request/response.
HttpRequest - The http request
HttpResponse - The http reponse
CancellationToken - The cancellation token associated with the current http request.
ClaimsPrincipal - The user associated with the request (HttpContext.User).

Custom Binding

There are 2 ways to customize parameter binding:

For route, query, and header binding sources, you may bind custom types by adding a static TryParse method to your type.
You can completely take over the binding process by implementing a BindAsync method on your type.

TryParse

The TryParse method must be of the form(s):

public static bool TryParse(string value, T out result);
public static bool TryParse(string value, IFormatProvider provider, T out result);

Example

app.MapGet("/map", (Point point) => $"Point: {point.X}, {point.Y}");

public class Point
{
    public double X { get; set; }
    public double Y { get; set; }

    public static bool TryParse(string? value, IFormatProvider? provider, out Point? point)
    {
        // Format is "(12.3,10.1)"
        var trimmedValue = value?.TrimStart('(').TrimEnd(')');
        var segments = trimmedValue?.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
        if (segments?.Length == 2
            && double.TryParse(segments[0], out var x)
            && double.TryParse(segments[1], out var y))
        {
            point = new Point { X = x, Y = y };
            return true;
        }

        point = null;
        return false;
    }
}

A request to /map?point=(12.3,10.1) returns:

Point: 12.3,10.1

BindAsync

The BindAsync method must be of the form:

public static ValueTask<T?> BindAsync(HttpContext context, ParameterInfo parameter);

Example

app.MapGet("/products", (PagingData pageData) => $"SortBy:{pageData.SortBy}, SortDirection:{pageData.SortDirection}, CurrentPage:{pageData.CurrentPage}");

public class PagingData
{
    public string? SortBy { get; init; }
    public SortDirection SortDirection { get; init; }
    public int CurrentPage { get; init; } = 1;

    public static ValueTask<PagingData?> BindAsync(HttpContext context, ParameterInfo parameter)
    {
        const string sortByKey = "sortBy";
        const string sortDirectionKey = "sortDir";
        const string currentPageKey = "page";

        Enum.TryParse<SortDirection>(context.Request.Query[sortDirectionKey], ignoreCase: true, out var sortDirection);
        int.TryParse(context.Request.Query[currentPageKey], out var page);
        page = page == 0 ? 1 : page;

        var result = new PagingData
        {
            SortBy = context.Request.Query[sortByKey],
            SortDirection = sortDirection,
            CurrentPage = page
        };

        return ValueTask.FromResult<PagingData?>(result);
    }
}

public enum SortDirection
{
    Default,
    Asc,
    Desc
}

Binding failures

When binding fails, the framework will log a debug message and it will return various status codes to the client depending on the failure mode.

Failure mode	Nullable Parameter Type	Binding Source	Status code
`{ParameterType}.TryParse` returns false	yes	route/query/header	400
`{ParameterType}.BindAsync` returns null	yes	custom	400
`{ParameterType}.BindAsync` throws	does not matter	custom	500
Failure to read JSON body	does not matter	body	400
Wrong content type (not application/json)	does not matter	body	415

Binding Precedence

The rules for determining a binding source from a parameter are as follows:

Explicit attribute defined on parameter (From* attributes) in the following order:
1. Route values (FromRoute)
2. Query string (FromQuery)
3. Header (FromHeader)
4. Body (FromBody)
5. Service (FromServices)
Special types
1. HttpContext
2. HttpRequest
3. HttpResponse
4. ClaimsPrincipal
5. CancellationToken
Parameter type has a valid BindAsync method.
Parameter type is a string or has a valid TryParse method.
1. If the parameter name exists in the route template e.g. app.Map("/todo/{id}", (int id) => {});, then it will be bound from the route.
2. It will be bound from the query string.
If the parameter type is a service provided by dependency injection, it will use that as the source.
The parameter is from the body.

Customizing JSON binding

The body binding source uses System.Text.Json for de-serialization. It is NOT possible to change this default but you can customize the binding using other techniques described in above sections. To customize JSON serializer options, you can use the following:

using Microsoft.AspNetCore.Http.Json;

var builder = WebApplication.CreateBuilder(args);

// Configure JSON options
builder.Services.Configure<JsonOptions>(options =>
{
    options.SerializerOptions.IncludeFields = true;
});

var app = builder.Build();

app.MapPost("/products", (Product product) => product);

app.Run();

class Product
{
    // These are public fields instead of properties
    public int Id;
    public string Name;
}

This configures both the input and output default JSON options.

Responses

Route handlers support 2 types of return values:

IResult based - This includes Task<IResult> and ValueTask<IResult>
string - This includes Task<string> and ValueTask<string>
T (Any other type) - This includes Task<T> and ValueTask<T>

Return value	Behavior	Content-Type
`IResult`	The framework calls `IResult.ExecuteAsync`	Decided by the `IResult` implementation
`string`	The framework writes the string directly to the response	`text/plain`
`T` (Any other type)	The framework will JSON serialize the response	`application/json`

Example: string return values

app.MapGet("/hello", () => "Hello World");

Example: JSON return values

app.MapGet("/hello", () => new { Message = "Hello World" });

Example: IResult return values

app.MapGet("/hello", () => Results.Ok(new { Message = "Hello World" }));

The following example uses the built-in result types to customize the response:

app.MapGet("/todos/{id}", (int id, TodoDb db) => 
    db.Todos.Find(id) is Todo todo 
        ? Results.Ok(todo)
        : Results.NotFound()
);

JSON

app.MapGet("/hello", () => Results.Json(new { Message = "Hello World" }));

Custom Status Code

app.MapGet("/405", () => Results.StatusCode(405));

Text

app.MapGet("/text", () => Results.Text("This is some text"));

Stream

var proxyClient = new HttpClient();
app.MapGet("/pokemon", async () => 
{
    var stream = await proxyClient.GetStreamAsync("http://myurl/pokedex.json")
    // Proxy the response as JSON
    return Results.Stream(stream, "application/json");
});

Redirect

app.MapGet("/old-path", () => Results.Redirect("/new-path"));

File

app.MapGet("/download", () => Results.File("foo.text"));

Built-in results

Common result helpers exist on the Microsoft.AspNetCore.Http.Results static class.

Description	Response type	Status Code	API
Write a JSON response with advanced options	application/json	200	`Results.Json`
Write a JSON response	application/json	200	`Results.Ok`
Write a text response	text/plain (default), configurable	200	`Results.Text`
Write the response as bytes	application/octet-stream (default), configurable	200	`Results.Bytes`
Write a stream of bytes to the response	application/octet-stream (default), configurable	200	`Results.Stream`
Stream a file to the response for download with the content-disposition header	application/octet-stream (default), configurable	200	`Results.File`
Set the status code to 404, with an optional JSON response	N/A	404	`Results.NotFound`
Set the status code to 204	N/A	204	`Results.NoContent`
Set the status code to 422, with an optional JSON response	N/A	422	`Results.UnprocessableEntity`
Set the status code to 400, with an optional JSON response	N/A	400	`Results.BadRequest`
Set the status code to 409, with an optional JSON response	N/A	409	`Results.Conflict`
Write a problem details JSON object to the response	N/A	500 (default), configurable	`Results.Problem`
Write a problem details JSON object to the response with validation errors	N/A	N/A, configurable	`Results.ValidationProblem`

Customizing results

Users can take control of responses by implementing a custom IResult type. Here's an example of an HTML result type:

namespace Microsoft.AspNetCore.Http;

static class ResultsExtensions
{
    public static IResult Html(this IResultExtensions resultExtensions, string html)
    {
        ArgumentNullException.ThrowIfNull(resultExtensions, nameof(resultExtensions));

        return new HtmlResult(html);
    }
}

class HtmlResult : IResult
{
    private readonly string _html;

    public HtmlResult(string html)
    {
        _html = html;
    }

    public Task ExecuteAsync(HttpContext httpContext)
    {
        httpContext.Response.ContentType = MediaTypeNames.Text.Html;
        httpContext.Response.ContentLength = Encoding.UTF8.GetByteCount(_html);
        return httpContext.Response.WriteAsync(_html);
    }
}

We recommend adding an extension method to Microsoft.AspNetCore.Http.IResultExtensions to make these custom results more discoverable.

app.MapGet("/html", () => Results.Extensions.Html(@$"<!doctype html>
<html>
    <head><title>miniHTML</title></head>
    <body>
        <h1>Hello World</h1>
        <p>The time on the server is {DateTime.Now:O}</p>
    </body>
</html>"));

Authorization

Routes can be protected using authorization policies. These can be declared via the Authorize attribute or by using the RequireAuthorization method.

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddAuthorization(o => o.AddPolicy("AdminsOnly", b => b.RequireClaim("admin", "true"));

var app = builder.Build();

app.UseAuthorization();

app.MapGet("/auth", [Authorize] () => "This endpoint requires authorization");

app.MapGet("/auth", () => "This endpoint requires authorization")
   .RequireAuthorization();

Authorization policies can be configured as well:

app.MapGet("/admin", [Authorize("AdminsOnly")] () => "This endpoint is for admins only");

app.MapGet("/admin", () => "This endpoint is for admins only")
   .RequireAuthorization("AdminsOnly");

Allowing unauthenticated users to an endpoint

It's also possible to allow any unauthenticated users to endpoints by using the AllowAnonymous attribute or the AllowAnonymous method.

app.MapGet("/login", [AllowAnonymous] () => "This endpoint is for admins only");

app.MapGet("/login", () => "This endpoint is for admins only")
   .AllowAnonymous();

CORS

Routes can be CORS enabled using CORS policies. These can be declared via the EnableCors attribute or by using the RequireCors method.

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddCors(options => options.AddPolicy("AnyOrigin", o => o.AllowAnyOrigin()));

var app = builder.Build();
app.UseCors();

app.MapGet("/cors", [EnableCors("AnyOrigin")] () => "This endpoint allows cross origin requests!");

app.MapGet("/cors", () => "This endpoint allows cross origin requests!")
   .RequireCors("AnyOrigin");

OpenAPI

It's possible to describe the OpenAPI specification for route handlers using Swashbuckle.

Below is an example of a typical ASP.NET Core application with OpenAPI suppport:

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen(c =>
{
    c.SwaggerDoc("v1", new() { Title = builder.Environment.ApplicationName, Version = "v1" });
});

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", $"{builder.Environment.ApplicationName} v1"));
}

Describing response types

app.MapGet("/api/products", (int id, ProductDb db) => db.Products.Find(id) is Product product ? Results.Ok(product) : Results.NotFound())
   .Produces<Product>(200)
   .Produces(404);

Exclude Open API description

app.MapGet("/skipme", () => { })
   .ExcludeFromDescription();

Add operation ids to Open API

app.MapGet("/api/products", (ProductDb db) => db.Products.ToListAsync())
   .WithName("GetProducts");

Add tags to the Open API description (used for grouping)

app.MapGet("/api/products", (ProductDb db) => db.Products.ToListAsync())
   .WithTags("ProductsGroup");

Describe request body

app.MapGet("/upload", async (HttpRequest req) =>
{
    if (!req.HasFormContentType)
    {
        return Results.BadRequest();
    }

    var form = await req.ReadFormAsync();
    var file = form.Files["file"];

    if (file is null)
    {
        return Results.BadRequest();
    }

    var uploads = Path.Combine(uploadsPath, file.FileName);
    await using var fileStream = File.OpenWrite(uploads);
    await using var uploadStream = file.OpenReadStream();
    await uploadStream.CopyToAsync(fileStream);

    return Results.NoContent();
})
.Accepts<IFormFile>("multipart/form-data");

Building libraries for ASP.NET Core

The existing .NET ecosystem has built extensibility around IServiceCollection, IHostBuilder and IWebHostBuilder. These properties are available on the WebApplicationBuilder as Services, Host and WebHost.

The WebApplication implements both Microsoft.AspNetCore.Builder.IApplicationBuilder and Microsoft.AspNetCore.Routing.IEndpointRouteBuilder.

We expect library authors to continue targeting IHostBuilder, IWebHostBuilder, IApplicationBuilder and IEndpointRouteBuilder when building ASP.NET Core specific components. This will ensure that your middleware, route handler, or other extensibility points continue to work across different hosting models.

Differences with ASP.NET Core MVC

No support for filters. i.e. IAsyncAuthorizationFilter, IAsyncActionFilter, IAsyncExceptionFilter, IAsyncResultFilter, IAsyncResourceFilter
No support for model binding. i.e. IModelBinderProvider, IModelBinder. Support can be added with a custom binding shim.
- No support for binding from forms. This includes binding IFormFile (this will be added in the future).
No built-in support for validation. i.e. IModelValidator
No support for application parts or the application model. There's no way to apply or build your own conventions.
No built-in view rendering support. We recommend using Razor Pages for rendering views.
No support for JsonPatch
No support for OData
No support for ApiVersioning, see this issue for more details.

hamburger1984/MinimalAPIs.md

Minimal APIs at a glance

WebApplication

Creating an application

Changing the port

Multiple ports

Reading the port from environment

Changing the ports via environment variables

Listening on all interfaces

HTTPS with development certificate

HTTPS with custom certificate

Reading the environment

Reading configuration

Logging

WebApplicationBuilder

Changing the content root, application name and environment

Changing the content root, application name and environment

Adding configuration providers

Reading configuration

Reading the environment

Adding logging providers

Adding services

Customizing the IHostBuilder

Customizing the IWebHostBuilder

Changing the web root

Custom dependency injection container

Adding Middleware

Developer Exception Page

ASP.NET Core Middleware

Routing

Route Handlers

Naming routes and link generation

Route Parameters

Wildcards/Catch all routes

Route constraints

Contraints

Parameter Binding

GET, HEAD, OPTIONS, DELETE

Other verbs (POST, PUT, PATCH, etc)

Explicit Parameter Binding

Optional parameters

Special types

Custom Binding

Binding failures

Binding Precedence

Customizing JSON binding

Responses

JSON

Custom Status Code

Text

Stream

Redirect

File

Built-in results

Customizing results

Authorization

Allowing unauthenticated users to an endpoint

CORS

OpenAPI

Describing response types

Exclude Open API description

Add operation ids to Open API

Add tags to the Open API description (used for grouping)

Describe request body

Building libraries for ASP.NET Core

Differences with ASP.NET Core MVC