MCP support

[noorbhatia]

Hey @mattt
I want to connect to MCP servers for dynamic tool discovery
Are there any plans for MCP support in AnyLanguageModel? If so, what's the intended approach?

[airy10]

You can have a look at this project for dynamically creating AnyLanguageModel Tools from MCP server tools : https://github.com/airy10/AppleFoundationMCPTool

[mattt]

@noorbhatia Yeah, that's a good question. Most of the documentation around Foundation Models focuses on tools and generable types declared at build time and compiled with macros. What you want for MCP is to build these dynamically at runtime, which I think is possible, but I haven't seen yet.

Here's a sketch of what I think that looks like at a high level:

/// A Tool backed by an MCP server tool discovered at runtime.
struct MCPTool: Tool {
    typealias Arguments = GeneratedContent
    typealias Output = String

    let name: String
    let description: String
    let parameters: GenerationSchema

    /// The closure that actually calls the MCP server.
    private let handler: @Sendable (GeneratedContent) async throws -> String

    init(
        name: String,
        description: String,
        inputSchema: JSONSchema,   // from MCP tools/list response
        handler: @escaping @Sendable (GeneratedContent) async throws -> String
    ) throws {
        self.name = name
        self.description = description
        self.handler = handler

        // Convert the MCP JSON Schema → DynamicGenerationSchema → GenerationSchema
        let dynamicSchema = convertToDynamicSchema(inputSchema, name: name)
        self.parameters = try GenerationSchema(
            root: dynamicSchema, 
            dependencies: []  // add deps if the schema has $defs/references
        )
    }

    func call(arguments: GeneratedContent) async throws -> String {
        try await handler(arguments)
    }
}

There are some finer details to work out wrt/schema conversion and MCP client statefulness, but this seems to be the general shape of a solution. Just a matter of documenting it and then deciding what additional affordances we want to provide — and how (custom API in AnyLanguageModel? separate library?)