mcpui-go

A Go SDK for the MCP-UI protocol, enabling MCP servers to return interactive UI resources that clients can render in sandboxed iframes.

Overview

MCP-UI extends the Model Context Protocol (MCP) to support rich, interactive user interfaces. This SDK provides the server-side implementation for Go-based MCP servers, allowing them to:

• Generate UI resources with HTML, URLs, or Remote DOM content
• Handle user interactions from UI components
• Send responses back to the UI layer
• Route actions to appropriate handlers

Installation

go get github.com/ironystock/mcpui-go@v0.1.0

Quick Start

Creating a Simple HTML Resource

package main

import (
    "encoding/json"
    "fmt"

    "github.com/ironystock/mcpui-go"
)

func main() {
    // Create HTML content
    content := &mcpui.HTMLContent{
        HTML: `<div style="padding: 20px; font-family: sans-serif;">
            <h1>Hello, World!</h1>
            <p>This is rendered in a sandboxed iframe.</p>
        </div>`,
    }

    // Create resource contents for MCP response
    rc, _ := mcpui.NewUIResourceContents("ui://greeting/hello", content)

    data, _ := json.MarshalIndent(rc, "", "  ")
    fmt.Println(string(data))
}

Handling UI Actions

package main

import (
    "context"
    "fmt"

    "github.com/ironystock/mcpui-go"
)

func main() {
    router := mcpui.NewRouter()

    // Handle tool actions
    router.HandleType(mcpui.ActionTypeTool, mcpui.WrapToolHandler(
        func(ctx context.Context, toolName string, params map[string]any) (any, error) {
            fmt.Printf("Tool called: %s\n", toolName)
            return map[string]string{"status": "executed"}, nil
        },
    ))

    // Handle specific resource
    router.HandleResource("ui://dashboard/main",
        func(ctx context.Context, req *mcpui.UIActionRequest) (*mcpui.UIActionResult, error) {
            return &mcpui.UIActionResult{Response: "dashboard handled"}, nil
        },
    )

    fmt.Println("Router configured")
}

Content Types

The SDK supports three types of UI content:

Type	Description	Use Case
HTMLContent	Inline HTML rendered via iframe srcdoc	Simple, self-contained UIs
URLContent	External URL rendered via iframe src	Existing web apps, complex UIs
RemoteDOMContent	Script-based UI using remote DOM	Dynamic, framework-based UIs

HTMLContent

Best for simple, self-contained UIs:

content := &mcpui.HTMLContent{
    HTML: `<div>
        <h1>Status Dashboard</h1>
        <p>All systems operational</p>
    </div>`,
}

URLContent

Best for existing web applications:

content := &mcpui.URLContent{
    URL: "https://example.com/dashboard",
}

RemoteDOMContent

Best for dynamic, framework-based UIs:

content := &mcpui.RemoteDOMContent{
    Script:    "React.createElement('div', null, 'Hello from React!')",
    Framework: mcpui.FrameworkReact,
}

Action Handling

When users interact with UI resources, the client sends UIAction messages. The SDK provides a flexible routing system:

router := mcpui.NewRouter()

// Handle by action type
router.HandleType(mcpui.ActionTypeTool, toolHandler)
router.HandleType(mcpui.ActionTypePrompt, promptHandler)
router.HandleType(mcpui.ActionTypeResource, resourceHandler)

// Handle by specific resource URI
router.HandleResource("ui://audio/mixer", audioHandler)
router.HandleResource("ui://scene/preview", sceneHandler)

// Route an action
result, err := router.Route(ctx, &mcpui.UIActionRequest{
    SourceURI: "ui://audio/mixer",
    Action:    action,
})

Response Messages

Send responses back to the UI:

// Acknowledge receipt
ack := mcpui.NewReceivedResponse(action.MessageID)

// Success response
resp := mcpui.NewSuccessResponse(action.MessageID, result)

// Error response
errResp := mcpui.NewErrorResponse(action.MessageID, err)

Documentation

• Content Types - HTMLContent, URLContent, RemoteDOMContent
• Resources - UIResource, UIResourceContents, validation
• Actions - UIAction types, payloads, parsing
• Responses - UIResponse builders, success/error handling
• Handlers - UIActionHandler, Router, typed wrappers
• Integration - How to integrate with MCP servers

Examples

See the examples directory for complete, runnable examples:

• basic - Minimal HTML resource example
• router - Router with multiple handlers
• remote-dom - Remote DOM with React framework
• action-handling - Complete action→response flow
• mcp-integration - Integration with MCP server

License

MIT License - see LICENSE for details.

Related

• MCP Go SDK - Official MCP Go SDK
• MCP-UI Specification - Protocol documentation
• agentic-obs - MCP server using this SDK