Minimal APIs overview

This document:

The minimal APIs consist of:

WebApplication

The following code is generated by an ASP.NET Core template:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

app.Run();

The preceding code can be created via dotnet new web on the command line or selecting the Empty Web template in Visual Studio.

The following code creates a WebApplication (app) without explicitly creating a WebApplicationBuilder:

var app = WebApplication.Create(args);

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

app.Run();

WebApplication.Create initializes a new instance of the WebApplication class with preconfigured defaults.

Working with ports

When a web app is created with Visual Studio or dotnet new, a Properties/launchSettings.json file is created that specifies the ports the app responds to. In the port setting samples that follow, running the app from Visual Studio returns an error dialog Unable to connect to web server 'AppName'. Run the following port changing samples from the command line.

The following sections set the port the app responds to.

var app = WebApplication.Create(args);

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

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

In the preceding code, the app responds to port 3000.

Multiple ports

In the following code, the app responds to port 3000 and 4000.

var app = WebApplication.Create(args);

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

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

app.Run();

Set the port from the command line

The following command makes the app respond to port 7777:

dotnet run --urls="https://localhost:7777"

If the Kestrel endpoint is also configured in the appsettings.json file, the appsettings.json file specified URL is used. For more information, see Kestrel endpoint configuration

Read the port from environment

The following code reads the port from the environment:

var app = WebApplication.Create(args);

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

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

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

The preferred way to set the port from the environment is to use the ASPNETCORE_URLS environment variable, which is shown in the following section.

Set the ports via the ASPNETCORE_URLS environment variable

The ASPNETCORE_URLS environment variable is available to set the port:

ASPNETCORE_URLS=http://localhost:3000

ASPNETCORE_URLS supports multiple URLs:

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

Listen on all interfaces

The following samples demonstrate listening on all interfaces

http://*:3000

var app = WebApplication.Create(args);

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

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

app.Run();

http://+:3000

var app = WebApplication.Create(args);

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

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

app.Run();

http://0.0.0.0:3000

var app = WebApplication.Create(args);

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

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

app.Run();

Listen on all interfaces using ASPNETCORE_URLS

The preceding samples can use ASPNETCORE_URLS

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

Specify HTTPS with development certificate

var app = WebApplication.Create(args);

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

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

app.Run();

For more information on the development certificate, see Trust the ASP.NET Core HTTPS development certificate on Windows and macOS.

Specify HTTPS using a custom certificate

The following sections show how to specify the custom certificate using the appsetting.json file and via configuration.

Specify the custom certificate with appsetting.json

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "Kestrel": {
    "Certificates": {
      "Default": {
        "Path": "cert.pem",
        "KeyPath": "key.pem"
      }
    }
  }
}

Specify the custom certificate via configuration

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();

Use 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();

Read 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();

For more information using the environment, see Use multiple environments in ASP.NET Core

Configuration

The following code reads from the configuration system:

var app = WebApplication.Create(args);

var message = app.Configuration["HelloKey"] ?? "Hello";

app.MapGet("/", () => message);

app.Run();

For more information, see Configuration in ASP.NET Core

Logging

The following code writes a message to the log on application startup:

var app = WebApplication.Create(args);

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

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

app.Run();

For more information, see Logging in .NET Core and ASP.NET Core

Access the Dependency Injection (DI) container

The following code shows how to get services from the DI container during application startup:


var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();
builder.Services.AddScoped<SampleService>();

var app = builder.Build();

app.MapControllers();

using (var scope = app.Services.CreateScope())
{
    var sampleService = scope.ServiceProvider.GetRequiredService<SampleService>();
    sampleService.DoSomething();
}

app.Run();

For more information, see Dependency injection in ASP.NET Core.

WebApplicationBuilder

This section contains sample code using WebApplicationBuilder.

Change the content root, application name, and environment

The following code sets the content root, application name, and environment:

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

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

var app = builder.Build();

WebApplication.CreateBuilder initializes a new instance of the WebApplicationBuilder class with preconfigured defaults.

For more information, see ASP.NET Core fundamentals

Change the content root, app name, and environment by environment variables or command line

The following table shows the environment variable and command-line argument used to change the content root, app name, and environment:

feature Environment variable Command-line argument
Application name ASPNETCORE_APPLICATIONNAME --applicationName
Environment name ASPNETCORE_ENVIRONMENT --environment
Content root ASPNETCORE_CONTENTROOT --contentRoot

Add configuration providers

The following sample adds the INI configuration provider:

var builder = WebApplication.CreateBuilder(args);

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

var app = builder.Build();

For detailed information, see File configuration providers in Configuration in ASP.NET Core.

Read configuration

By default the WebApplicationBuilder reads configuration from multiple sources, including:

  • appSettings.json and appSettings.{environment}.json
  • Environment variables
  • The command line

For a complete list of configuration sources read, see Default configuration in Configuration in ASP.NET Core

var builder = WebApplication.CreateBuilder(args);

var message = builder.Configuration["HelloKey"] ?? "Hello";

var app = builder.Build();

app.MapGet("/", () => message);

app.Run();

Read the environment

The following code reads HelloKey from configuration and displays the value at the / endpoint. If the configuration value is null, "Hello" is assigned to message:

var builder = WebApplication.CreateBuilder(args);

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

var app = builder.Build();

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

app.Run();

Add logging providers

var builder = WebApplication.CreateBuilder(args);

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

var app = builder.Build();

app.MapGet("/", () => "Hello JSON console!");

app.Run();

Add 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();

Customize 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();

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

app.Run();

Customize the IWebHostBuilder

Extension methods on IWebHostBuilder can be accessed using the WebApplicationBuilder.WebHost property.

var builder = WebApplication.CreateBuilder(args);

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

var app = builder.Build();

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

app.Run();

Change the web root

By default, the web root is relative to the content root in the wwwroot folder. Web root is where the static files middleware looks for static files. Web root can be changed with WebHostOptions, the command line, or with the UseWebRoot method:

var builder = WebApplication.CreateBuilder(args);

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

var app = builder.Build();

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

app.Run();

Custom dependency injection (DI) container

The following example uses Autofac:

var builder = WebApplication.CreateBuilder(args);

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

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

var app = builder.Build();

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

app.Run();

For more information, see ASP.NET Core Middleware

Developer exception page

WebApplication.CreateBuilder initializes a new instance of the WebApplicationBuilder class with preconfigured defaults. The developer exception page is enabled in the preconfigured defaults. When the following code is run in the development environment, navigating to / renders a friendly page that shows the exception.

var builder = WebApplication.CreateBuilder(args);

var app = builder.Build();

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

app.Run();

ASP.NET Core Middleware

The following table lists some of the middleware frequently used with minimal APIs.

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

Request handling

The following sections cover routing, parameter binding, and responses.

Routing

A configured WebApplication supports Map{Verb} and MapMethods:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

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

app.Run();

Route Handlers

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

Lambda expression

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

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

app.MapGet("/", handler);

app.Run();

Local function

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

app.MapGet("/", LocalFunction);

app.Run();

Instance method

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

var handler = new HelloHandler();

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

app.Run();

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

Static method

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

app.Run();

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

Routes can be given names in order to generate URLs to the route. Using a named route avoids having to hard code paths in an app:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

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

app.Run();

The preceding code displays The link to the hello route is /hello from the / endpoint.

Route names are inferred from method names if specified:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

string Hi() => "Hello there";
app.MapGet("/hello", Hi);

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

app.Run();

REVIEW: {linker.GetPathByName("Hi", values: null)} is null in the preceding code.

NOTE: Route names are case sensitive.

Route names:

  • Must be globally unique.
  • Are used as the OpenAPI operation id when OpenAPI support is enabled. See the OpenAPI section for more details.

Route Parameters

Route parameters can be captured as part of the route pattern definition:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

app.Run();

The preceding code returns The user id is 3 and book id is 7 from the URI /users/3/books/7.

The route handler can declare the parameters to capture. When a request is made a route with parameters declared to capture, the parameters are parsed and passed to the handler. This makes it easy to capture the values in a type safe way. In the preceding code, userId and bookId are both int.

In the preceding code, if either route value cannot be converted to an int, an exception is thrown. The GET request /users/hello/books/3 throws the following exception:

BadHttpRequestException: Failed to bind parameter "int userId" from "hello".

Wildcard and catch all routes

The following catch all route returns Routing to hello from the `/posts/hello' endpoint:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

app.Run();

Route constraints

Route constraints constrain the matching behavior of a route.

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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}");

app.Run();

The following table demonstrates the preceding route templates and their behavior:

Route Template Example Matching URI
/todos/{id:int} /todos/1
/todos/{text} /todos/something
/posts/{slug:regex(^[a-z0-9_-]+$)} /posts/mypost

For more information, see Route constraint reference in Routing in ASP.NET Core.

Parameter Binding

Parameter binding is the process of converting 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 explicit or inferred based on 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 is not natively supported in .NET 6.

GET, HEAD, OPTIONS, DELETE

The HTTP methods GET, HEAD, OPTIONS, and DELETE don't implicitly bind from body. Bind explicitly with [FromBody] or read from the request body. All other binding sources are supported.

NOTE: To support the case of GET with a body, directly read it from the HttpRequest.

var builder = WebApplication.CreateBuilder(args);

// Added as service
builder.Services.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

POST, PUT, PATCH, etc

var builder = WebApplication.CreateBuilder(args);

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

var app = builder.Build();

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 are bound from.

using Microsoft.AspNetCore.Mvc;

var builder = WebApplication.CreateBuilder(args);

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

var app = builder.Build();


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

class Service { }

record Person(string Name, int Age);
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 in .NET 6.

Optional parameters

Parameters declared in route handlers are treated as required:

  • If a request matches the route, the route handler only runs if all required parameters are provided in the request.
  • Failure to provide all required parameters results in an error.
var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

app.Run();
URI result
/products?pageNumber=3 3 returned
/products BadHttpRequestException: Required parameter "int pageNumber" was not provided from query string.
/products/1 HTTP 404 error, no matching route

To make pageNumber optional, define the type as optional or provide a default value:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

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

app.MapGet("/products2", ListProducts);

app.Run();
URI result
/products?pageNumber=3 3 returned
/products 1 returned
/products2 1 returned

The preceding nullable and default value applies to all sources:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

app.Run();

The preceding code calls the method with a null product if no request body is sent.

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

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

app.Run();
URI result
/products?pageNumber=3 3 returned
/products 1 returned
/products/two BadHttpRequestException: Failed to bind parameter "Nullable<int> pageNumber" from "two".

See the Binding Failures section for more information.

Special types

The following types are bound without explicit attributes:

  • HttpContext : The context which holds all the information about the current HTTP request or response.
  • HttpRequest : The HTTP request
  • HttpResponse : The HTTP response
  • CancellationToken : The cancellation token associated with the current http request.
  • ClaimsPrincipal : The user associated with the request (HttpContext.User).

Custom Binding

There are two ways to customize parameter binding:

  1. For route, query, and header binding sources, bind custom types by adding a static TryParse method for the type.
  2. Control the binding process by implementing a BindAsync method on a type.

TryParse

TryParse has two APIs:

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

The following code displays Point: 12.3, 10.1 with the URI /map?Point=12.3,10.1:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

// GET /map?Point=12.3,10.1
app.MapGet("/map", (Point point) => $"Point: {point.X}, {point.Y}");

app.Run();

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;
    }
}

BindAsync

BindAsync has the following APIs:

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

The following code displays SortBy:xyz, SortDirection:Desc, CurrentPage:99 with the URI /products?SortBy=xyz&SortDir=Desc&Page=99:

using System.Reflection;

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

// GET /products?SortBy=xyz&SortDir=Desc&Page=99
app.MapGet("/products", (PagingData pageData) => $"SortBy:{pageData.SortBy}, " +
       $"SortDirection:{pageData.SortDirection}, CurrentPage:{pageData.CurrentPage}");

app.Run();

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 logs a debug message and returns 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 deserialize 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:

  1. 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]
  2. Special types
    1. HttpContext
    2. HttpRequest
    3. HttpResponse
    4. ClaimsPrincipal
    5. CancellationToken
  3. Parameter type has a valid BindAsync method.
  4. 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's bound from the route.
    2. Bound from the query string.
  5. If the parameter type is a service provided by dependency injection, it uses that service as the source.
  6. The parameter is from the body.

Customize JSON binding

The body binding source uses System.Text.Json for de-serialization. It is not possible to change this default, but the binding can be customized using other techniques described previously. To customize JSON serializer options, use code similar to 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, not properties.
    public int Id;
    public string? Name;
}

The preceding code:

  • Configures both the input and output default JSON options.
  • Returns the following JSON
    {
      "id": 1,
      "name": "Joe Smith"
    }
    
    When posting
    {
      "Id": 1,
      "Name": "Joe Smith"
    }
    

Responses

Route handlers support the following types of return values:

  1. IResult based - This includes Task<IResult> and ValueTask<IResult>
  2. string - This includes Task<string> and ValueTask<string>
  3. 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 return values

string return values

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

JSON return values

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

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("/api/todoitems/{id}", async (int id, TodoDb db) =>
         await db.Todos.FindAsync(id) 
         is Todo todo
         ? Results.Ok(todo) 
         : Results.NotFound())
   .Produces<Todo>(200)
   .Produces(404);

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 builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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

app.Run();

Redirect

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

File

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

Built-in results

Common result helpers exist in 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

Applications can control responses by implementing a custom IResult type. The following code is an example of an HTML result type:

using System.Net.Mime;
using System.Text;
static class ResultsExtensions
{
    public static IResult Html(this IResultExtensions resultExtensions, string html)
    {
        ArgumentNullException.ThrowIfNull(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.

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

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>"));

app.Run();

Authorization

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

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using WebRPauth.Data;

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

var connectionString = builder.Configuration.GetConnectionString("DefaultConnection");
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();

builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
    .AddEntityFrameworkStores<ApplicationDbContext>();

var app = builder.Build();

app.UseAuthorization();

app.MapGet("/auth", [Authorize] () => "This endpoint requires authorization.");
app.MapGet("/", () => "This endpoint doesn't require authorization.");
app.MapGet("/Identity/Account/Login", () => "Sign in page at this endpoint.");

app.Run();

The preceding code can be written with RequireAuthorization:

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

The following sample uses policy-based authorization:

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using WebRPauth.Data;

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

var connectionString = builder.Configuration.GetConnectionString("DefaultConnection");
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();

builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
    .AddEntityFrameworkStores<ApplicationDbContext>();

var app = builder.Build();

app.UseAuthorization();

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

app.MapGet("/admin2", () => "The /admin2 endpoint is for admins only.")
   .RequireAuthorization("AdminsOnly");

app.MapGet("/", () => "This endpoint doesn't require authorization.");
app.MapGet("/Identity/Account/Login", () => "Sign in page at this endpoint.");

app.Run();

Allow unauthenticated users to access an endpoint

The [AllowAnonymous] allows unauthenticated users to access endpoints:

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


app.MapGet("/login2", () => "This endpoint also for admins only.")
   .AllowAnonymous();

CORS

Routes can be CORS enabled using CORS policies. CORS can be declared via the [EnableCors] attribute or by using the RequireCors method. The following samples enable CORS:

const string MyAllowSpecificOrigins = "_myAllowSpecificOrigins";

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddCors(options =>
{
    options.AddPolicy(name: MyAllowSpecificOrigins,
                      builder =>
                      {
                          builder.WithOrigins("http://example.com",
                                              "http://www.contoso.com");
                      });
});

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

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

app.Run();
using Microsoft.AspNetCore.Cors;

const string MyAllowSpecificOrigins = "_myAllowSpecificOrigins";

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddCors(options =>
{
    options.AddPolicy(name: MyAllowSpecificOrigins,
                      builder =>
                      {
                          builder.WithOrigins("http://example.com",
                                              "http://www.contoso.com");
                      });
});

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

app.MapGet("/cors", [EnableCors(MyAllowSpecificOrigins)] () => 
                           "This endpoint allows cross origin requests!");
app.MapGet("/cors2", () => "This endpoint allows cross origin requests!")
                     .RequireCors(MyAllowSpecificOrigins);

app.Run();

For more information, see Enable Cross-Origin Requests (CORS) in ASP.NET Core

OpenAPI

An app can describe the OpenAPI specification for route handlers using Swashbuckle.

The following code is a typical ASP.NET Core app with OpenAPI support:

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"));
}

app.MapGet("/swag", () => "Hello Swagger!");

app.Run();

Exclude Open API description

In the following sample, the /skipme endpoint is excluded from generating an OpenAPI description:

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.MapGet("/swag", () => "Hello Swagger!");
app.MapGet("/skipme", () => "Skipping Swagger.")
                    .ExcludeFromDescription();

app.Run();

Describe response types

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

app.MapGet("/api/todoitems/{id}", async (int id, TodoDb db) =>
         await db.Todos.FindAsync(id) 
         is Todo todo
         ? Results.Ok(todo) 
         : Results.NotFound())
   .Produces<Todo>(200)
   .Produces(404);

Add operation ids to Open API

app.MapGet("/todoitems2", async (TodoDb db) =>
    await db.Todos.ToListAsync())
    .WithName("GetToDoItems");

Add tags to the Open API description

The following code uses an OpenAPI grouping tag:

app.MapGet("/todoitems", async (TodoDb db) =>
    await db.Todos.ToListAsync())
    .WithTags("TodoGroup");