Tool Calling

Tools extend the capabilities of AI models by giving them the ability to call your functions. Models trained for tool calling can respond with a request to invoke a tool, and Genkit handles the execution automatically.

Defining a tool

@SuppressWarnings("unchecked")
Tool<Map<String, Object>, Map<String, Object>> weatherTool = genkit.defineTool(
    "getWeather",
    "Gets the current weather for a location",
    Map.of(
        "type", "object",
        "properties", Map.of(
            "location", Map.of(
                "type", "string",
                "description", "The city name"
            )
        ),
        "required", new String[]{"location"}
    ),
    (Class<Map<String, Object>>) (Class<?>) Map.class,
    (ctx, input) -> {
        String location = (String) input.get("location");
        return Map.of(
            "location", location,
            "temperature", "72°F",
            "conditions", "sunny"
        );
    });

Using tools in generation

Pass tools to generate() — the tool execution loop is handled automatically:

ModelResponse response = genkit.generate(
    GenerateOptions.builder()
        .model("openai/gpt-4o")
        .prompt("What's the weather in Paris?")
        .tools(List.of(weatherTool))
        .build());

System.out.println(response.getText());
// Output: "The weather in Paris is currently 72°F and sunny."

How it works

1. You define tools with a name, description, and input schema
2. The model receives the tool definitions alongside your prompt
3. If the model decides to call a tool, Genkit automatically executes it
4. The tool result is sent back to the model for final response generation

Typed tools

You can also define tools with typed input/output classes:

Tool<RecipeRequest, MenuItem> recipeGen = genkit.defineTool(
    "generateRecipe",
    "Generates a recipe",
    (ctx, request) -> new MenuItem(...),
    RecipeRequest.class,
    MenuItem.class
);

Next steps

DotPrompt Manage prompts as template files

Multi-Agent Build multi-agent orchestration

MCP Plugin Connect to MCP tool servers