Open Source C# API Clients

RestSharp is probably the most popular HTTP client library for .NET. Featuring automatic serialization and deserialization, request and response type detection, variety of authentications and other useful features, it is being used by hundreds of thousands of projects. RestSharp passed over 32 million downloads on NuGet, with average daily download count of 10,000. It's being used by many popular OSS projects, including Roslyn and Swagger. The main purpose of RestSharp is to make synchronous and asynchronous calls to remote resources over HTTP. As the name suggests, the main audience of RestSharp are developers who use REST APIs. However, RestSharp can call any API over HTTP (but not HTTP/2), as long as you have the resource URI and request parameters that you want to send comply with W3C HTTP standards. RestSharp can take care of serializing the request body to JSON or XML and deserialize the response. It can also form a valid request URI based on different parameter kinds.

It nudges you towards the REPR Design Pattern (Request-Endpoint-Response) for convenient & maintainable endpoint creation with virtually no boilerplate. Performance is on par with Minimal APIs. It's faster, uses less memory and does around 45k more requests per second than a MVC Controller in our benchmarks. Convenient business logic validation & error responses. Easy access to environment & configuration settings. Supports policy/permission/role/claim based security. In-process pub/sub event notifications (with auto discovery). Declarative security policy building (within each endpoint). Easy Server-Sent-Events for real-time data streaming. Supports any IOC container compatible with ASP.NET. Convenient integration testing (route-less & strongly-typed). Constructor & property injection of endpoint dependencies. Built-in uncaught exception handler. Easy model binding from route/query/json body/claims/forms/headers. Supports swagger/serilog/etc.

Microsoft Kiota is an open-source tool that generates client libraries from OpenAPI descriptions, making it easier to interact with RESTful APIs. It is designed to work seamlessly with Microsoft Graph and other API ecosystems, providing strongly typed SDKs in multiple programming languages. Kiota simplifies API consumption by automating the creation of client libraries, reducing the manual effort needed to integrate with APIs.

SugarRestSharp is a .NET C# SugarCRM CE 6.x API client. It is a Restful CRUD client that implements the SugarCRM module Create, Read, Update and Delete functionalities. SugarRestSharp implements following SugarCRM REST API method calls: oauth_access, get_entry, get_entry_list, set_entry, set_entries.