---
title: Overview of OpenAPI support in ASP.NET Core API apps
author: rick-anderson
description: Learn about OpenAPI features in ASP.NET Core.
ms.author: wpickett
monikerRange: '>= aspnetcore-6.0'
ms.date: 8/02/2024
uid: fundamentals/openapi/overview
---

# OpenAPI support in ASP.NET Core API apps

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:::moniker range=">= aspnetcore-9.0"

ASP.NET Core supports the generation of OpenAPI documents in controller-based and minimal APIs apps.
The [OpenAPI specification](https://spec.openapis.org/oas/latest.html) is a programming language-agnostic standard for documenting HTTP APIs. This standard is supported in ASP.NET Core apps through a combination of built-in APIs and open-source libraries. There are three key aspects to OpenAPI integration in an application:

* Generating information about the endpoints in the app.
* Gathering the information into a format that matches the OpenAPI schema.
* Exposing the generated OpenAPI document via a visual UI or a serialized file.

ASP.NET Core apps provide built-in support for generating information about endpoints in an app via the `Microsoft.AspNetCore.OpenApi` package.

<!-- TODO: Merge content from controllers overview here, as appropriate -->

The following code is generated by the ASP.NET Core minimal web API template and uses OpenAPI:

[!code-csharp[](~/fundamentals/minimal-apis/9.0-samples/WebMinOpenApi/Program.cs?name=snippet_default&highlight=5,9-12)]

In the preceding highlighted code:

* `AddOpenApi` registers services required for OpenAPI document generation into the application's DI container.
* `MapOpenApi` adds an endpoint into the application for viewing the OpenAPI document serialized into JSON. The OpenAPI endpoint is restricted to the development environment to minimize the risk of exposing sensitive information and reduce the vulnerabilities in production.

<a name="openapinuget"></a>

## `Microsoft.AspNetCore.OpenApi` NuGet package

The [`Microsoft.AspNetCore.OpenApi`](https://www.nuget.org/packages/Microsoft.AspNetCore.OpenApi/) package provides the following features:

* Support for generating OpenAPI documents at run time and accessing them via an endpoint on the application.
* Support for "transformer" APIs that allow modifying the generated document.

To use the `Microsoft.AspNetCore.OpenApi` package, add it as a PackageReference to a project file:

[!code-xml[](~/fundamentals/minimal-apis/9.0-samples/WebMinOpenApi/projectFile.xml?highlight=15)]

To learn more about the `Microsoft.AspNetCore.OpenApi` package, see <xref:fundamentals/openapi/aspnetcore-openapi>.

## `Microsoft.Extensions.ApiDescription.Server` NuGet package

The [`Microsoft.Extensions.ApiDescription.Server`](https://www.nuget.org/packages/Microsoft.Extensions.ApiDescription.Server/) package provides support for generating OpenAPI documents at build time and serializing them.

To use `Microsoft.Extensions.ApiDescription.Server`, add it as a PackageReference to a project file.
Document generation at build time is enabled by setting the `OpenApiGenerateDocuments` property.
By default, the generated OpenAPI document is saved to the `obj` directory, but you can customize
the output directory by setting the `OpenApiDocumentsDirectory` property.

[!code-xml[](~/fundamentals/minimal-apis/9.0-samples/WebMinOpenApi/projectFile.xml?highlight=9-12,16-19)]

## ASP.NET Core OpenAPI source code on GitHub

* [AddOpenApi](https://github.com/dotnet/aspnetcore/blob/main/src/OpenApi/src/Extensions/OpenApiServiceCollectionExtensions.cs)
* [OpenApiDocumentService](https://github.com/dotnet/aspnetcore/blob/main/src/OpenApi/src/Services/OpenApiDocumentService.cs)
* [OpenApiOptions](https://github.com/dotnet/aspnetcore/blob/main/src/OpenApi/src/Services/OpenApiOptions.cs)

## Additional Resources

* <xref:fundamentals/minimal-apis/security>

:::moniker-end

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