Building the Future of APIs: Mike Kistler's Insights on OpenAPI and MCP

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This episode of The Modern .NET Show is supported, in part, by RJJ Software's Strategic Technology Consultation Services. If you're an SME (Small to Medium Enterprise) leader wondering why your technology investments aren't delivering, or you're facing critical decisions about AI, modernization, or team productivity, let's talk.

Show Notes

"And we talk about that contract. We say, "this is your contract. This Open API definition that you have is the contract for your service." And in the end, that's how customers interact with Azure is through APIs. And so it's important to have that contract so that customers know how things work, how to use them, hopefully how to use them easily, right?"— Mike Kistler

Hey everyone, and welcome back to The Modern .NET Show; the premier .NET podcast, focusing entirely on the knowledge, tools, and frameworks that all .NET developers should have in their toolbox. I'm your host Jamie Taylor, bringing you conversations with the brightest minds in the .NET ecosystem.

Today, we're joined by Mike Kistler to talk about two topics (we usually only tackle one topic per episode, so you're getting a bonus with this episode): Open API and both MCP and the MCP SDK for C#.

We started our conversation by focussing on Open API, as this is a passion of Mike's. We talked about what it is, how you've likely already been using it with any ASP .NET Core WebAPIs that you've worked on, and how the latest versions of ASP .NET Core can generate a lot of the Open API specification for you without having to add lots and lots of metadata an attributes.

Pro tip: If you've been using the Swagger UI in your applications, you've been using Open API.

"And when the LLM decides that it wants to use an MCP tool or access an MCP resource, it doesn't go and do that directly. It comes back to the MCP host and asks the MCP host to call a tool with a particular set of parameters, or to access an MCP resource. And at first, when I saw this in the MCP architecture, I thought, "boy, that's clunky. Why not have the LLM just call these things directly?" And there's a deliberate reason why it was done this way."— Mike Kistler

We then pivoted over to talking about MCP (or Model Context Protocol) which is a rapidly evolving standard for creating your own agents and applications which can communicate with or be instructed by, LLMs. We talked about how the MCP standard works, and how the standard is written in such a way that there's always a human in the loop. We also talked about how you can build your own MCP servers using the MCP SDK for C#.

It's worth pointing out that both MCP and Open API are evolving standards. While Open API tends to evolve with a much more relaxed pace, the MCP standard (having not even reached a year old when we recorded) uses the date as it's version number. And Mike actually references the latest version of the MCP spec in our conversation, which will give you a clue as to when we recorded it.

Before we jump in, a quick reminder: if The Modern .NET Show has become part of your learning journey, please consider supporting us through Patreon or Buy Me A Coffee. Every contribution helps us continue bringing you these in-depth conversations with industry experts. You'll find all the links in the show notes.

Anyway, without further ado, let's sit back, open up a terminal, type in `dotnet new podcast` and we'll dive into the core of Modern .NET.

Full Show Notes

The full show notes, including links to some of the things we discussed and a full transcription of this episode, can be found at: https://dotnetcore.show/season-8/building-the-future-of-apis-mike-kistlers-insights-on-openapi-and-mcp

Useful Links:

• OpenAPI
• API Blueprint
• RAML
• ProducesResponseType attribute
• Minimal API
• TypedResults
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