Recursive AI
LibraryC#Available

onemodelcontext

A .NET SDK for the Model Context Protocol®, client and server, in C#. Declare tools with attributes, serve them over stdio or Streamable HTTP, and connect to any server, old revision or new, through one API.

Open source, MIT or Apache-2.0, made by Recursive AI. Version 1.0.1 is on NuGet. The core depends on the .NET base class library only.

dotnet add package RecursiveAI.OneModelContext
Getting started Docs GitHub NuGet

A quick look

A tool is a method with [Tool] on it. The generator writes its schema from the signature and doc comments; one call serves it, and one call connects to it.

The output shown is from a run on 1.0.1 from NuGet. The server is abridged here; Getting started has both programs whole.

Getting started
Glossary.cs, Program.csC#
public partial class Glossary
{
    /// <summary>Looks up a term.</summary>
    /// <param name="term">The word or phrase to define.</param>
    [Tool(ReadOnly = true)]
    public string Define(string term) => …;
}
 
await ModelContext.ServeAsync(new Glossary());   // stdio
 
// The client, in another program:
await using var client = await ModelContext.ConnectAsync(
    "dotnet run --project ../GlossaryServer");
Console.WriteLine($"protocol {client.ProtocolVersion} ({client.Era} era)");
// protocol 2026-07-28 (Modern era)
 
var result = await client.CallToolAsync("define",
    new { term = "idempotent" });
Console.WriteLine(result.Text);
// idempotent: Safe to repeat: doing it twice has
// the same effect as doing it once.
What it does

Both protocol eras, one API

“The stateless 2026-07-28 revision first, and one legacy codec for 2024-11-05 through 2025-11-25. A client negotiates the era per server; a server answers both on one stdio stream or endpoint.”

Era negotiation

stdio and Streamable HTTP

“stdio and any duplex Stream; Streamable HTTP as a client, as a host-agnostic server core, on a small built-in HTTP/1.1 listener (loopback by default) and on ASP.NET Core with MapModelContext; the deprecated HTTP+SSE transport as a client fallback.”

Streamable HTTP client

The built-in listener

A small HTTP/1.1 server on Socket, “for local tools and command-line programs.” ModelContext.ServeHttpAsync starts one on the loopback address, and every size and time limit is an option with a documented default.

Listener limits

Tools, resources and prompts

“Declared with attributes or registered while the server runs.” In the README’s words, “The generator writes each tool’s JSON Schema 2020-12 from the signature and its doc comments, and an AOT-safe invoker.”

Tool schemas

Resource server

For an HTTP server that requires sign-in: “protected resource metadata, challenges, step-up, audience checks; JWT/JWKS, introspection, static-token and delegate validators.”

Resource server

OAuth client

“A full OAuth 2.1 client, Client Credentials and Enterprise-Managed Authorization.” It follows “the 2026-07-28 authorization pages (with the 2025-03-26, 2025-06-18 and 2025-11-25 differences), OAuth 2.1, RFC 9728, RFC 8414, OpenID Connect Discovery, RFC 7636, RFC 8707 and RFC 9207.”

OAuth client

Embedded authorization server

“An embedded AuthorizationServer whose login and consent stay with the host.” In the docs’ words, “Signing a user in and asking for consent is a callback into your application, and the server never renders a login page itself.”

Authorization server

Extensions

“A public extension mechanism, MCP Apps, and Tasks, Skills and Server Cards, which are [Experimental] until their specifications are stable.”

Extensions

Safe by default

“Every size, depth and time limit is a documented default on a public option.” Tokens are never logged, and no request that carries a credential follows a redirect.

Limits and defaults
How it was checked

The conformance suite

In the repository’s words, it “is checked against the protocol’s official conformance suite, run as a black box: it is installed from its published package and driven through its command line.” The suite is @modelcontextprotocol/conformance 0.2.0-alpha.12.

RevisionScenarios that pass
2026-07-28Server 35 of 35, client 33 of 33
2025-11-25Server 34 of 34, client 19 of 19
2025-06-18Server 27 of 27, client 5 of 5
2025-03-26Server 1 of 1, client 2 of 2
ExtensionsServer 13 of 13, client 7 of 10
  • Server. Run by gate-server.sh “on both hosts (listener and aspnetcore), with the same result on each.” For the server extensions (Tasks, Skills), “the suite itself skips tasks-status-notifications.”
  • Client. Run by gate-client.sh with the conformance client. The 3 that fail, auth/dpop, auth/dpop-nonce and auth/wif-jwt-bearer, “test authorization extensions this library does not implement.”
  • Authorization server. The suite’s two scenarios “pass at every --spec-version they apply to.”
  • 2024-11-05. “The suite lists no scenarios for 2024-11-05; that revision is covered by the interop harness.”
Conformance, scenario by scenario
Status and limits

What 1.0.1 is, and isn’t

  • Status. “Status: 1.0. The public API is stable and checked by package validation. Tasks, Skills and Server Cards follow experimental MCP extensions and are marked [Experimental] until those extensions are stable.”
  • Deprecated features. “Sampling, Roots and Logging are implemented and marked [Obsolete] (diagnostic IDs OMC0001-OMC0003), following the revision that deprecates them.”
  • The listener is for local use. “For a server on the internet, host the endpoint in a web framework.”
  • HTTP+SSE. “This transport is client-only; the library never serves it.”
  • DPoP. Not implemented. “DPoP will be added in a minor release once it reaches Beta or Stable.”
  • The quick path. Tools from lambdas are “a reflection quick path that writes the same schemas and is annotated as not trim- or AOT-safe.”
  • Token storage. A client keeps its tokens in memory, an owner-only file, EF Core or OneLite; “there is no keychain package.”
The overview

Packages

Go further

GitHub NuGet Getting started All docs Samples Coming from the official C# SDK Changelog

Model Context Protocol® is a registered trademark of LF Projects, LLC. OneModelContext is an independent project and is not affiliated with or endorsed by LF Projects, LLC or the Model Context Protocol project.