aspnetcore/tutorials/first-web-api.md
By Tim Deschryver and Rick Anderson
:::moniker range=">= aspnetcore-9.0"
This tutorial teaches the basics of building a controller-based web API that uses a database. Another approach to creating APIs in ASP.NET Core is to create Minimal APIs. For help with choosing between Minimal APIs and controller-based APIs, see xref:fundamentals/apis. For a tutorial on creating a Minimal API, see xref:tutorials/min-web-api.
This tutorial creates the following API:
| API | Description | Request body | Response body |
|---|---|---|---|
GET /api/todoitems | Get all to-do items | None | Array of to-do items |
GET /api/todoitems/{id} | Get an item by ID | None | To-do item |
POST /api/todoitems | Add a new item | To-do item | To-do item |
PUT /api/todoitems/{id} | Update an existing item | To-do item | None |
DELETE /api/todoitems/{id} | Delete an item | None | None |
The following diagram shows the design of the app.
A NuGet package must be added to support the database used in this tutorial.
Microsoft.EntityFrameworkCore.InMemory.Open the integrated terminal.
Change directories (cd) to the folder that will contain the project folder.
Run the following commands:
dotnet new webapi --use-controllers -o TodoApi
cd TodoApi
dotnet add package Microsoft.EntityFrameworkCore.InMemory
code -r .
These commands:
The project template creates a WeatherForecast API with support for OpenAPI.
Press Ctrl+F5 to run without the debugger.
Visual Studio launches a terminal window and displays the URL of the running app. The API is hosted at https://localhost:<port>, where <port> is a randomly chosen port number set at the project creation.
...
info: Microsoft.Hosting.Lifetime[14]
Now listening on: https://localhost:7260
info: Microsoft.Hosting.Lifetime[14]
Now listening on: http://localhost:7261
info: Microsoft.Hosting.Lifetime[0]
Application started. Press Ctrl+C to shut down.
...
<kbd>Ctrl</kbd>+click the HTTPS URL in the output to test the web app in a browser. There's no endpoint at https://localhost:<port>, so the browser returns HTTP 404 Not Found.
Append /weatherforecast to the URL to test the WeatherForecast API.
The browser displays JSON similar to the following example:
[
{
"date": "2025-07-16",
"temperatureC": 52,
"temperatureF": 125,
"summary": "Mild"
},
{
"date": "2025-07-17",
"temperatureC": 36,
"temperatureF": 96,
"summary": "Warm"
},
{
"date": "2025-07-18",
"temperatureC": 39,
"temperatureF": 102,
"summary": "Cool"
},
{
"date": "2025-07-19",
"temperatureC": 10,
"temperatureF": 49,
"summary": "Bracing"
},
{
"date": "2025-07-20",
"temperatureC": -1,
"temperatureF": 31,
"summary": "Chilly"
}
]
Run the app:
Run the following command to start the app on the https profile:
dotnet run --launch-profile https
The output shows messages similar to the following, indicating that the app is running and awaiting requests:
...
info: Microsoft.Hosting.Lifetime[14]
Now listening on: https://localhost:{port}
...
<kbd>Ctrl</kbd>+click the HTTPS URL in the output to test the web app in a browser.
The default browser is launched to https://localhost:<port>, where <port> is the randomly chosen port number displayed in the output. There's no endpoint at https://localhost:<port>, so the browser returns HTTP 404 Not Found.
Append /weatherforecast to the URL to test the WeatherForecast API. The browser displays JSON similar to the following example:
[
{
"date": "2025-07-16",
"temperatureC": 52,
"temperatureF": 125,
"summary": "Mild"
},
{
"date": "2025-07-17",
"temperatureC": 36,
"temperatureF": 96,
"summary": "Warm"
},
{
"date": "2025-07-18",
"temperatureC": 39,
"temperatureF": 102,
"summary": "Cool"
},
{
"date": "2025-07-19",
"temperatureC": 10,
"temperatureF": 49,
"summary": "Bracing"
},
{
"date": "2025-07-20",
"temperatureC": -1,
"temperatureF": 31,
"summary": "Chilly"
}
]
This tutorial uses Endpoints Explorer and .http files to test the API.
There are many available web API testing tools to choose from, and you can follow this tutorial's introductory API test steps with your preferred tool.
This tutorial utilizes the .NET package NSwag.AspNetCore, which integrates Swagger tools for generating a testing UI adhering to the OpenAPI specification:
For more information on using OpenAPI and NSwag with ASP.NET, see xref:tutorials/web-api-help-pages-using-swagger.
Run the following command:
dotnet add package NSwag.AspNetCore
The previous command adds the NSwag.AspNetCore package, which contains tools to generate Swagger documents and UI. Because our project is using OpenAPI, we only use the NSwag package to generate the Swagger UI.
Program.cs, add the following highlighted code::::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi_SwaggerVersion/Program.cs" id="snippet_UseSwagger" highlight="6-9":::
The previous code enables the Swagger middleware for serving the generated JSON document using the Swagger UI. Swagger is only enabled in a development environment. Enabling Swagger in a production environment could expose potentially sensitive details about the API's structure and implementation.
The app uses the OpenAPI document generated by OpenApi, located at /openapi/v1.json, to generate the UI.
View the generated OpenAPI specification for the WeatherForecast API while the project is running by navigating to https://localhost:<port>/openapi/v1.json in your browser.
The OpenAPI specification is a document in JSON format that describes the structure and capabilities of your API, including endpoints, request/response formats, parameters, and more. It's essentially a blueprint of your API that can be used by various tools to understand and interact with your API.
A model is a set of classes that represent the data that the app manages. The model for this app is the TodoItem class.
Models.Models folder and select Add > Class. Name the class TodoItem and select Add.:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi/Models/TodoItem.cs":::
Models.TodoItem.cs file to the Models folder with the following code::::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi_SwaggerVersion/Models/TodoItem.cs":::
The Id property functions as the unique key in a relational database.
Model classes can go anywhere in the project, but the Models folder is used by convention.
The database context is the main class that coordinates Entity Framework functionality for a data model. This class is created by deriving from the xref:Microsoft.EntityFrameworkCore.DbContext?displayProperty=fullName class.
Right-click the Models folder and select Add > Class. Name the class TodoContext and click Add.
Enter the following code:
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi/Models/TodoContext.cs":::
Add a TodoContext.cs file to the Models folder.
Enter the following code:
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi_SwaggerVersion/Models/TodoContext.cs":::
In ASP.NET Core, services such as the DB context must be registered with the dependency injection (DI) container. The container provides the service to controllers.
Update Program.cs with the following highlighted code:
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi/Program.cs" highlight="1-2,8-9":::
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi_SwaggerVersion/Program.cs" highlight="1-2,8-9":::
The preceding code:
using directives.Right-click the Controllers folder.
Select Add > :::no-loc text="New Scaffolded Item":::.
Select API Controller with actions, using Entity Framework, and then select Add.
In the Add API Controller with actions, using Entity Framework dialog:
If the scaffolding operation fails, select Add to try scaffolding a second time.
This step adds the Microsoft.VisualStudio.Web.CodeGeneration.Design and Microsoft.EntityFrameworkCore.Tools NuGet packages to the project.
These packages are required for scaffolding.
Make sure that all of your changes so far are saved.
TodoAPI project folder.
Run the following commands:dotnet add package Microsoft.VisualStudio.Web.CodeGeneration.Design
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.SqlServer
dotnet add package Microsoft.EntityFrameworkCore.Tools
dotnet tool uninstall -g dotnet-aspnet-codegenerator
dotnet tool install -g dotnet-aspnet-codegenerator
dotnet tool update -g dotnet-aspnet-codegenerator
The preceding commands:
dotnet-aspnet-codegenerator) after uninstalling any possible previous version.For Linux, add the .NET tools directory to the system path with the following command:
echo 'export PATH=$HOME/.dotnet/tools:$PATH' >> ~/.bashrc
source ~/.bashrc
Build the project.
Run the following command:
dotnet aspnet-codegenerator controller -name TodoItemsController -async -api -m TodoItem -dc TodoContext -outDir Controllers
The preceding command scaffolds the TodoItemsController.
The generated code:
[ApiController] attribute. This attribute indicates that the controller responds to web API requests. For information about specific behaviors that the attribute enables, see xref:web-api/index.TodoContext) into the controller. The database context is used in each of the CRUD methods in the controller.The ASP.NET Core templates for:
[action] in the route template.[action] in the route template.When the [action] token isn't in the route template, the action name (method name) isn't included in the endpoint. That is, the action's associated method name isn't used in the matching route.
Update the return statement in the PostTodoItem to use the nameof operator:
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi/Controllers/TodoItemsController.cs" id="snippet_Create":::
The preceding code is an HTTP POST method, as indicated by the [HttpPost] attribute. The method gets the value of the TodoItem from the body of the HTTP request.
For more information, see Attribute routing with Http[Verb] attributes.
The xref:Microsoft.AspNetCore.Mvc.ControllerBase.CreatedAtAction%2A method:
HTTP 201 is the standard response for an HTTP POST method that creates a new resource on the server.Location header specifies the URI of the newly created to-do item. For more information, see 10.2.2 201 Created.GetTodoItem action to create the Location header's URI. The C# nameof keyword is used to avoid hard-coding the action name in the CreatedAtAction call.<a name="post7"></a>
Select View > Other Windows > Endpoints Explorer.
Right-click the POST endpoint and select Generate request.
A new file is created in the project folder named TodoApi.http, with contents similar to the following example:
@TodoApi_HostAddress = https://localhost:49738
POST {{TodoApi_HostAddress}}/api/todoitems
Content-Type: application/json
{
//TodoItem
}
###
###) line is a request delimiter: what comes after it is for a different request.The POST request expects a TodoItem. To define the todo, replace the //TodoItem comment with the following JSON:
{
"name": "walk dog",
"isComplete": true
}
The TodoApi.http file should now look like the following example, but with your port number:
@TodoApi_HostAddress = https://localhost:7260
Post {{TodoApi_HostAddress}}/api/todoitems
Content-Type: application/json
{
"name": "walk dog",
"isComplete": true
}
###
Run the app.
Select the Send request link that is above the POST request line.
The POST request is sent to the app and the response is displayed in the Response pane.
With the app still running, in the browser, navigate to https://localhost:<port>/swagger to display the API testing page generated by Swagger. Click on TodoItems to expand the operations.
On the Swagger API testing page, select Post /api/todoitems > Try it out.
Note that the Request body field contains a generated example format reflecting the parameters for the API.
In the request body enter JSON for a to-do item, without specifying the optional id:
{
"name": "walk dog",
"isComplete": true
}
Select Execute.
Swagger provides a Responses pane below the Execute button.
Note a few of the useful details:
id was set to 1.HTTP status code was returned, indicating that the request was successfully processed and resulted in the creation of a new resource.Test the app by calling the GET endpoints from a browser or by using Endpoints Explorer. The following steps are for Endpoints Explorer.
In Endpoints Explorer, right-click the first GET endpoint, and select Generate request.
The following content is added to the TodoApi.http file:
GET {{TodoApi_HostAddress}}/api/todoitems
###
Select the Send request link that is above the new GET request line.
The GET request is sent to the app and the response is displayed in the Response pane.
The response body is similar to the following JSON:
[
{
"id": 1,
"name": "walk dog",
"isComplete": true
}
]
In Endpoints Explorer, right-click the /api/todoitems/{id} GET endpoint and select Generate request.
The following content is added to the TodoApi.http file:
@id=0
GET {{TodoApi_HostAddress}}/api/todoitems/{{id}}
###
Assign {@id} to 1 (instead of 0).
Select the Send request link that is above the new GET request line.
The GET request is sent to the app and the response is displayed in the Response pane.
The response body is similar to the following JSON:
{
"id": 1,
"name": "walk dog",
"isComplete": true
}
Test the app by calling the endpoints from a browser or Swagger.
In Swagger select GET /api/todoitems > Try it out > Execute.
Alternatively, call GET /api/todoitems from a browser by entering the URI https://localhost:<port>/api/todoitems. For example, https://localhost:7260/api/todoitems
The call to GET /api/todoitems produces a response similar to the following:
[
{
"id": 1,
"name": "walk dog",
"isComplete": true
}
]
Call GET /api/todoitems/{id} in Swagger to return data from a specific id:
1 and select Execute.Alternatively, call GET /api/todoitems from a browser by entering the URI https://localhost:<port>/api/todoitems/1. For example, https://localhost:7260/api/todoitems/1
The response is similar to the following:
{
"id": 1,
"name": "walk dog",
"isComplete": true
}
Two GET endpoints are implemented:
GET /api/todoitemsGET /api/todoitems/{id}The previous section showed an example of the /api/todoitems/{id} route.
Follow the POST instructions to add another todo item, and then test the /api/todoitems route using Swagger.
This app uses an in-memory database. If the app is stopped and started, the preceding GET request doesn't return any data. If no data is returned, POST data to the app.
The [HttpGet] attribute denotes a method that responds to an HTTP GET request. The URL path for each method is constructed as follows:
Start with the template string in the controller's Route attribute:
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi/Controllers/TodoItemsController.cs" id="snippet_Route" highlight="1":::
Replace [controller] with the name of the controller, which by convention is the controller class name minus the "Controller" suffix. For this sample, the controller class name is TodoItemsController, so the controller name is "TodoItems". ASP.NET Core routing is case insensitive.
If the [HttpGet] attribute has a route template (for example, [HttpGet("products")]), append that to the path. This sample doesn't use a template. For more information, see Attribute routing with Http[Verb] attributes.
In the following GetTodoItem method, "{id}" is a placeholder variable for the unique identifier of the to-do item. When GetTodoItem is invoked, the value of "{id}" in the URL is provided to the method in its id parameter.
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi/Controllers/TodoItemsController.cs" id="snippet_GetByID" highlight="1-2":::
The return type of the GetTodoItems and GetTodoItem methods is ActionResult<T> type. ASP.NET Core automatically serializes the object to JSON and writes the JSON into the body of the response message. The response code for this return type is 200 OK, assuming there are no unhandled exceptions. Unhandled exceptions are translated into 5xx errors.
ActionResult return types can represent a wide range of HTTP status codes. For example, GetTodoItem can return two different status values:
item results in an HTTP 200 response.Examine the PutTodoItem method:
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi/Controllers/TodoItemsController.cs" id="snippet_Update" :::
PutTodoItem is similar to PostTodoItem, except it uses HTTP PUT. The response is 204 (No Content). According to the HTTP specification, a PUT request requires the client to send the entire updated entity, not just the changes. To support partial updates, use HTTP PATCH.
This sample uses an in-memory database that must be initialized each time the app is started. There must be an item in the database before you make a PUT call. Call GET to ensure there's an item in the database before making a PUT call.
Use the PUT method to update the TodoItem that has Id = 1 and set its name to "feed fish". Note the response is HTTP 204 No Content.
In Endpoints Explorer, right-click the PUT endpoint, and select Generate request.
The following content is added to the TodoApi.http file:
PUT {{TodoApi_HostAddress}}/api/todoitems/{{id}}
Content-Type: application/json
{
//TodoItem
}
###
In the PUT request line, replace {{id}} with 1.
Replace the //TodoItem placeholder with the following lines:
PUT {{TodoApi_HostAddress}}/api/todoitems/1
Content-Type: application/json
{
"id": 1,
"name": "feed fish",
"isComplete": false
}
Select the Send request link that is above the new PUT request line.
The PUT request is sent to the app and the response is displayed in the Response pane. The response body is empty, and the status code is 204.
Use Swagger to send a PUT request:
Select Put /api/todoitems/{id} > Try it out.
Set the id field to 1.
Set the request body to the following JSON:
{
"id": 1,
"name": "feed fish",
"isComplete": false
}
Select Execute.
Examine the DeleteTodoItem method:
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApi/Controllers/TodoItemsController.cs" id="snippet_Delete" :::
Use the DELETE method to delete the TodoItem that has Id = 1. Note the response is HTTP 204 No Content.
In Endpoints Explorer, right-click the DELETE endpoint and select Generate request.
A DELETE request is added to TodoApi.http.
Replace {{id}} in the DELETE request line with 1. The DELETE request should look like the following example:
DELETE {{TodoApi_HostAddress}}/api/todoitems/{{id}}
###
Select the Send request link for the DELETE request.
The DELETE request is sent to the app and the response is displayed in the Response pane. The response body is empty, and the status code is 204.
Use Swagger to send a DELETE request:
Select DELETE /api/todoitems/{id} > Try it out.
Set the ID field to 1 and select Execute.
The DELETE request is sent to the app and the response is displayed in the Responses pane. The response body is empty, and the Server response status code is 204.
There are many other tools that can be used to test web APIs, for example:
<!-- Verify https://go.microsoft.com/fwlink/?linkid=2123754 goes to this H2. Verify the latest released version is on top so this anchor works --><a name="over-post"></a>
Currently the sample app exposes the entire TodoItem object. Production apps typically limit the data that's input and returned using a subset of the model. There are multiple reasons behind this, and security is a major one. The subset of a model is usually referred to as a Data Transfer Object (DTO), input model, or view model. DTO is used in this tutorial.
A DTO may be used to:
To demonstrate the DTO approach, update the TodoItem class to include a secret field:
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApiDTO/Models/TodoItem.cs" highlight="8" :::
The secret field needs to be hidden from this app, but an administrative app could choose to expose it.
Verify you can post and get the secret field.
Create a DTO model in a Models/TodoItemDTO.cs file:
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApiDTO/Models/TodoItemDTO.cs" :::
Update the TodoItemsController to use TodoItemDTO:
:::code language="csharp" source="~/tutorials/first-web-api/samples/9.0/TodoApiDTO/Controllers/TodoItemsController.cs" :::
Verify you can't post or get the secret field.
See Tutorial: Call an ASP.NET Core web API with JavaScript.
See Video: Beginner's Series to: Web APIs.
<a name="auth"></a>
For information on deploying to Azure, see Quickstart: Deploy an ASP.NET web app.
View or download sample code for this tutorial. See how to download.
For more information, see the following resources:
:::moniker-end