Openapi.client

Created with ❤ in Poland by lepo.co and the awesome open-source community.
OpenAPI Client is a modern toolkit for developers working with OpenAPI/Swagger specifications. It provides multiple tools to simplify the creation, inspection, validation, and integration of OpenAPI clients across .NET projects and MCP (Model Context Protocol) environments.

🧰 What's in this repo?

This repository contains a suite of OpenAPI tools designed to support different workflows:

Tool	Description
🧠 .NET Source Generator	Generates C# HTTP clients directly from OpenAPI JSON/YAML files at build time.
💻 .NET CLI Tool	Command-line tool to generate clients from OpenAPI definitions manually.
🛰️ MCP Server	Containerized server with built-in tools for working with OpenAPI specs.

🚀 MCP Server Tools

The MCP Server is the central piece of this toolkit. It runs as a standalone container or inside an MCP setup and exposes tools for working with OpenAPI documents.

🛠️ Available Server Tools

Tool	Description
get_list_of_operations	Lists all operation IDs from a given OpenAPI or Swagger JSON document.
get_known_responses	Lists all known responses for given operation IDs from a OpenAPI or Swagger JSON document.
validate_document	Validates the structure and syntax of an OpenAPI JSON document.
generate_curl_command	Generates a cURL command for a specific operation ID.
create_csharp_snippet	Creates a simple HTTP request for a given operation ID.

🐳 Run the server with Docker

Build the image:

docker buildx build ./ -t mcp/openapi --no-cache
# or
dotnet publish ./src/OpenApi.Client.Mcp/OpenApi.Client.Mcp.csproj -c Release /t:PublishContainer

Run the container:

docker run -d -i --rm --name mcp-openapi mcp/openapi
# or for HTTP mode:
docker run -d -i --rm --name mcp-openapi mcp/openapi -e MODE=Http -p 64622:8080

Example MCP config (.mcp.json):

{
  "servers": {
    "openapi": {
      "type": "stdio",
      "command": "docker",
      "args": ["run", "-i", "--rm", "mcp/openapi"]
    }
  },
  "inputs": []
}

📦 NuGet Package (Source Generator)

OpenApiClient is available as NuGet package on NuGet.org:
https://www.nuget.org/packages/OpenApiClient

Install the package to enable automatic OpenAPI client generation:

dotnet add package OpenApiClient

, or package manager console:

NuGet\Install-Package OpenApiClient

In your .csproj:

<ItemGroup>
  <AdditionalFiles Include="google.youtube.api.json" />
</ItemGroup>

Define a client:

[OpenApiClient("google.youtube.api")]
public partial class YouTubeClient;

Use it:

var client = new YouTubeClient(new HttpClient());
var subs = await client.SubscribersCountAsync("mychannel", CancellationToken.None);

Known limitations

Since we are using the generated internal OpenApiAttribute as a marker, conflicts may occur when we use InternalsVisibleTo.

We found the use of nullable essential, so C# 8.0 is required.

💻 .NET CLI Tool

Generate OpenAPI clients from the terminal:

dotnet tool install --global OpenApiClient.Cli

dotnet openapi generate ./google.youtube.api.json --output ./clients/YouTubeClient.cs --namespace Google.YouTube --classname YouTubeClient

OpenAPI

OpenAPI specification is available at:
https://github.com/OAI/OpenAPI-Specification

Code of Conduct

This project has adopted the code of conduct defined by the Contributor Covenant to clarify expected behavior in our community.

License

OpenAPI Client is free and open source software licensed under MIT License. You can use it in private and commercial projects.
Keep in mind that you must include a copy of the license in your project.