experimental-ext-interceptors/go/sdk

MCP Interceptors - Go Implementation

Go implementation of the MCP Interceptor Extension based on SEP-2624.

Note: Currently the MCP SDK is vendored, in-order to add the Protocol Methods needed for interceptors.

Quick Start

mcpServer := mcp.NewServer(&mcp.Implementation{
    Name:    "my-server",
    Version: "0.1.0",
}, nil)

// Create an extension and register interceptors.
ext := extension.New()

// Register a validator that blocks dangerous tool calls.
ext.AddInterceptor(&interceptors.Validator{
    Metadata: interceptors.Metadata{
        Name: "block-dangerous",
        Hooks: []interceptors.Hook{{
            Events: []string{interceptors.EventToolsCall},
            Phase:  interceptors.PhaseRequest,
        }},
        Mode: interceptors.ModeEnforce,
    },
    Handler: func(_ context.Context, inv *interceptors.Invocation) (*interceptors.ValidationResult, error) {
        raw := inv.Payload.(json.RawMessage)
        var params struct{ Name string `json:"name"` }
        json.Unmarshal(raw, &params)
        // validate the request...
        return &interceptors.ValidationResult{Valid: true}, nil
    },
})

// Install on the server and create a chain for middleware.
ext.Install(mcpServer)
chain, err := ext.LocalChain(ctx, mcpServer)
mcpServer.AddReceivingMiddleware(gomiddleware.Middleware(chain))

mcpServer.Run(context.Background(), &mcp.StdioTransport{})

See examples/ for complete working examples.

Documentation

• DESIGN.md — architecture, execution model, integration with the go-sdk.
• PERFORMANCE.md — per-request cost model, allocation summary, and optimization notes.
• CONFORMANCE.md — SEP conformance status.

Package API documentation is available via go doc:

go doc github.com/modelcontextprotocol/ext-interceptors/go/sdk/interceptors