# Integrate REST APIs with OpenAPI

<div class="language-support-tag">
  <span class="lst-supported">Supported in ADK</span><span class="lst-python">Python v0.1.0</span>
</div>

ADK simplifies interacting with external REST APIs by automatically generating callable tools directly from an [OpenAPI Specification (v3.x)](https://swagger.io/specification/). This eliminates the need to manually define individual function tools for each API endpoint.

!!! tip "Core Benefit"
    Use `OpenAPIToolset` to instantly create agent tools (`RestApiTool`) from your existing API documentation (OpenAPI spec), enabling agents to seamlessly call your web services.

## Key components

* **`OpenAPIToolset`**: This is the primary class you'll use. You initialize it with your OpenAPI specification, and it handles the parsing and generation of tools.
* **`RestApiTool`**: This class represents a single, callable API operation (like `GET /pets/{petId}` or `POST /pets`). `OpenAPIToolset` creates one `RestApiTool` instance for each operation defined in your spec.

## How it works

The process involves these main steps when you use `OpenAPIToolset`:

1. **Initialization & Parsing**:
    * You provide the OpenAPI specification to `OpenAPIToolset` either as a Python dictionary, a JSON string, or a YAML string.
    * The toolset internally parses the spec, resolving any internal references (`$ref`) to understand the complete API structure.

2. **Operation Discovery**:
    * It identifies all valid API operations (e.g., `GET`, `POST`, `PUT`, `DELETE`) defined within the `paths` object of your specification.

3. **Tool Generation**:
    * For each discovered operation, `OpenAPIToolset` automatically creates a corresponding `RestApiTool` instance.
    * **Tool Name**: Derived from the `operationId` in the spec (converted to `snake_case`, max 60 chars). If `operationId` is missing, a name is generated from the method and path.
    * **Tool Description**: Uses the `summary` or `description` from the operation for the LLM.
    * **API Details**: Stores the required HTTP method, path, server base URL, parameters (path, query, header, cookie), and request body schema internally.

4. **`RestApiTool` Functionality**: Each generated `RestApiTool`:
    * **Schema Generation**: Dynamically creates a `FunctionDeclaration` based on
   the operation's parameters and request body. This schema tells the LLM how
   to call the tool (what arguments are expected).
    * **Execution**: When the LLM calls the tool, the tool constructs the HTTP
  request, including the URL, headers, query parameters, and body, using the
  LLM's arguments and the OpenAPI specification. The tool handles
  authentication if configured, and executes the API call asynchronously using the `httpx` library.
    * **Response Handling**: Returns the API response (typically JSON) back to the agent flow.

5. **Authentication**: You can configure global authentication (like API keys or
   OAuth - see [Authentication](/tools-custom/authentication/) for details)
   when initializing `OpenAPIToolset`. This authentication configuration is
   automatically applied to all generated `RestApiTool` instances.

## Usage workflow

Follow these steps to integrate an OpenAPI spec into your agent:

1. **Obtain Spec**: Get your OpenAPI specification document (e.g., load from a `.json` or `.yaml` file, fetch from a URL).
2. **Instantiate Toolset**: Create an `OpenAPIToolset` instance, passing the spec content and type (`spec_str`/`spec_dict`, `spec_str_type`). Provide authentication details (`auth_scheme`, `auth_credential`) if required by the API.

    ```python
    from google.adk.tools.openapi_tool.openapi_spec_parser.openapi_toolset import OpenAPIToolset

    # Example with a JSON string
    openapi_spec_json = '...' # Your OpenAPI JSON string
    toolset = OpenAPIToolset(spec_str=openapi_spec_json, spec_str_type="json")

    # Example with a dictionary
    # openapi_spec_dict = {...} # Your OpenAPI spec as a dict
    # toolset = OpenAPIToolset(spec_dict=openapi_spec_dict)
    ```

3. **Add to Agent**: Include the retrieved tools in your `LlmAgent`'s `tools` list.

    ```python
    from google.adk.agents import LlmAgent

    my_agent = LlmAgent(
        name="api_interacting_agent",
        model="gemini-flash-latest", # Or your preferred model
        tools=[toolset], # Pass the toolset
        # ... other agent config ...
    )
    ```

4. **Instruct agent**: Update your agent's instructions to inform it about the new API capabilities and the names of the tools it can use (e.g., `list_pets`, `create_pet`). The tool descriptions generated from the spec will also help the LLM.
5. **Run agent**: Execute your agent using the `Runner`. When the LLM determines it needs to call one of the APIs, it will generate a function call targeting the appropriate `RestApiTool`, which will then handle the HTTP request automatically.

## See it in action

This example demonstrates generating tools from a simple Pet Store OpenAPI spec (using `httpbin.org` for mock responses) and interacting with them via an agent.

???+ "Code: Pet Store API"

    ```python title="openapi_example.py"
    --8<-- "examples/python/snippets/tools/openapi_tool.py"
    ```