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Function Calling with Custom Tools

Enable AI models to use external functions by defining tool schemas using OpenAI format. Models can then call these functions automatically based on user requests. 
curl --location 'http://localhost:8080/v1/chat/completions' \
--header 'Content-Type: application/json' \
--data '{
    "model": "openai/gpt-4o-mini",
    "messages": [
        {"role": "user", "content": "What is 15 + 27? Use the calculator tool."}
    ],
    "tools": [
        {
            "type": "function",
            "function": {
                "name": "calculator",
                "description": "A calculator tool for basic arithmetic operations",
                "parameters": {
                    "type": "object",
                    "properties": {
                        "operation": {
                            "type": "string",
                            "description": "The operation to perform",
                            "enum": ["add", "subtract", "multiply", "divide"]
                        },
                        "a": {
                            "type": "number",
                            "description": "The first number"
                        },
                        "b": {
                            "type": "number",
                            "description": "The second number"
                        }
                    },
                    "required": ["operation", "a", "b"]
                }
            }
        }
    ],
    "tool_choice": "auto"
}'
Response includes tool calls: 
{
    "choices": [{
        "message": {
            "role": "assistant", 
            "tool_calls": [{
                "id": "call_abc123",
                "type": "function",
                "function": {
                    "name": "calculator",
                    "arguments": "{\"operation\":\"add\",\"a\":15,\"b\":27}"
                }
            }]
        }
    }]
}

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Connecting to MCP Servers

Connect to Model Context Protocol (MCP) servers to give AI models access to external tools and services without manually defining each function.
MCP Configuration Interface
  1. Go to http://localhost:8080
  2. Navigate to “MCP Clients” in the sidebar
  3. Click “Add MCP Client”
  4. Enter server details and save
Read more about MCP connections and advanced end to end tool execution in the MCP Features section.

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Tool Choice Options

Control how the AI uses tools: 
# Force use of specific tool
"tool_choice": {
    "type": "function",
    "function": {"name": "calculator"}
}

# Let AI decide automatically (default)
"tool_choice": "auto"

# Disable tool usage
"tool_choice": "none"

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Next Steps

Now that you understand tool calling, explore these related topics:

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Essential Topics

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Advanced Topics