Tutorial 15

Content Types

Demonstrates all MCP content types: **text**, **image**, and **embedded resource**.

Demonstrates all MCP content types: text, image, and embedded resource.

How It Works

MCP tool responses can contain different content types. The framework handles serialization based on what the handler returns.

Examples

Text Content

Raw tool handlers return []byte which is wrapped as TextContent:

tool, _ := finemcp.NewTool("text-example",
    func(ctx context.Context, input []byte) ([]byte, error) {
        return []byte("Hello, this is plain text content"), nil
    },
    finemcp.WithDescription("Returns text content"),
)

Image Content

Typed tools can return image data with base64 encoding:

tool, _ := finemcp.NewTypedTool("image-example",
    func(ctx context.Context, input struct{}) (string, error) {
        return "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==", nil
    },
    finemcp.WithDescription("Returns an image"),
)

Embedded Resource Content

Tools can embed resource content within their response:

tool, _ := finemcp.NewTool("embedded-example",
    func(ctx context.Context, input []byte) ([]byte, error) {
        return []byte(`{"uri": "file:///data.json", "text": "{\"key\": \"value\"}"}`), nil
    },
    finemcp.WithDescription("Returns embedded resource content"),
)

Testing with curl

go run ./15-content-types

curl -X POST http://localhost:8080 -H "Content-Type: application/json" -d '{
  "jsonrpc": "2.0", "id": 1, "method": "initialize",
  "params": { "protocolVersion": "2025-03-26", "clientInfo": { "name": "curl", "version": "1.0.0" }, "capabilities": {} }
}'

# Text content
curl -X POST http://localhost:8080 -H "Content-Type: application/json" -d '{
  "jsonrpc": "2.0", "id": 2, "method": "tools/call",
  "params": { "name": "text-example" }
}'

# Image content
curl -X POST http://localhost:8080 -H "Content-Type: application/json" -d '{
  "jsonrpc": "2.0", "id": 3, "method": "tools/call",
  "params": { "name": "image-example" }
}'

# Embedded resource
curl -X POST http://localhost:8080 -H "Content-Type: application/json" -d '{
  "jsonrpc": "2.0", "id": 4, "method": "tools/call",
  "params": { "name": "embedded-example" }
}'