Function calling with the PromptKit SDK.

What You’ll Learn

• Defining tools in pack files
• Registering tool handlers with OnTool()
• Automatic JSON serialization
• Multiple tool handlers with OnTools()

Prerequisites

• Go 1.21+
• OpenAI API key

Running the Example

export OPENAI_API_KEY=your-key
go run .

Code Overview

conv, err := sdk.Open("./tools.pack.json", "assistant")
if err != nil {
    log.Fatal(err)
}
defer conv.Close()

// Register tool handlers
conv.OnTool("get_time", func(args map[string]any) (any, error) {
    timezone := args["timezone"].(string)
    return map[string]string{
        "time":     "14:30:00",
        "timezone": timezone,
    }, nil
})

conv.OnTool("get_weather", func(args map[string]any) (any, error) {
    city := args["city"].(string)
    return map[string]any{
        "city":        city,
        "temperature": 22.5,
        "conditions":  "Sunny",
    }, nil
})

// LLM will automatically call tools when needed
resp, _ := conv.Send(ctx, "What's the weather in London?")
fmt.Println(resp.Text())

Pack File Structure

Tools must be:

1. Defined in the tools section
2. Listed in the prompt’s tools array

{
  "prompts": {
    "assistant": {
      "system_template": "You are a helpful assistant...",
      "tools": ["get_weather", "get_time"]
    }
  },
  "tools": {
    "get_weather": {
      "name": "get_weather",
      "description": "Get current weather for a city",
      "parameters": {
        "type": "object",
        "properties": {
          "city": { "type": "string" },
          "country": { "type": "string" }
        },
        "required": ["city", "country"]
      }
    }
  }
}

Handler Signature

func(args map[string]any) (any, error)

• args: Parameters from the LLM (matches tool schema)
• return: Any JSON-serializable value, or error

Multiple Tools

Register all handlers at once:

conv.OnTools(map[string]sdk.ToolHandler{
    "get_time":    timeHandler,
    "get_weather": weatherHandler,
    "search":      searchHandler,
})

Return Structs

Return Go structs - they’re automatically serialized:

type Weather struct {
    City        string  `json:"city"`
    Temperature float64 `json:"temperature"`
}

conv.OnTool("get_weather", func(args map[string]any) (any, error) {
    return Weather{City: "London", Temperature: 18.5}, nil
})

Key Concepts

1. Declarative Tools - Define in pack, implement in code
2. Auto Serialization - Return any Go value
3. Error Handling - Return errors to inform the LLM
4. Tool Calls - LLM decides when to use tools

Next Steps

• Hello Example - Basic conversation
• Streaming Example - Real-time responses
• HITL Example - Human-in-the-loop approval