Tools

Here, we’re going to see advanced tool usage.

• Tools
  • What is a tool, and how to build one?
  • Share your tool to the Hub
  • Import a Space as a tool
  • Use LangChain tools
  • Manage your agent’s toolbox
  • Use a collection of tools

What is a tool, and how to build one?

A tool is mostly a function that an LLM can use in an agentic system.

But to use it, the LLM will need to be given an API: name, tool description, input types and descriptions, output type.

So it cannot be only a function. It should be a class.

So at core, the tool is a class that wraps a function with metadata that helps the LLM understand how to use it.

Here’s how it looks:

from smolagents import Tool

class HFModelDownloadsTool(Tool):
    name = "model_download_counter"
    description = """
    This is a tool that returns the most downloaded model of a given task on the Hugging Face Hub.
    It returns the name of the checkpoint."""
    inputs = {
        "task": {
            "type": "string",
            "description": "the task category (such as text-classification, depth-estimation, etc)",
        }
    }
    output_type = "string"

    def forward(self, task: str):
        from huggingface_hub import list_models

        model = next(iter(list_models(filter=task, sort="downloads", direction=-1)))
        return model.id

model_downloads_tool = HFModelDownloadsTool()

The custom tool subclasses Tool to inherit useful methods. The child class also defines:

• An attribute name, which corresponds to the name of the tool itself. The name usually describes what the tool does. Since the code returns the model with the most downloads for a task, let’s name it model_download_counter.
• An attribute description is used to populate the agent’s system prompt.
• An inputs attribute, which is a dictionary with keys "type" and "description". It contains information that helps the Python interpreter make educated choices about the input.
• An output_type attribute, which specifies the output type. The types for both inputs and output_type should be Pydantic formats, they can be either of these: ~AUTHORIZED_TYPES().
• A forward method which contains the inference code to be executed.

And that’s all it needs to be used in an agent!

There’s another way to build a tool. In the guided_tour, we implemented a tool using the @tool decorator. The tool() decorator is the recommended way to define simple tools, but sometimes you need more than this: using several methods in a class for more clarity, or using additional class attributes.

In this case, you can build your tool by subclassing Tool as described above.

Share your tool to the Hub

You can share your custom tool to the Hub by calling push_to_hub() on the tool. Make sure you’ve created a repository for it on the Hub and are using a token with read access.

model_downloads_tool.push_to_hub("{your_username}/hf-model-downloads", token="<YOUR_HUGGINGFACEHUB_API_TOKEN>")

For the push to Hub to work, your tool will need to respect some rules:

• All method are self-contained, e.g. use variables that come either from their args.
• As per the above point, all imports should be defined directky within the tool’s functions, else you will get an error when trying to call save() or push_to_hub() with your custom tool.
• If you subclass the __init__ method, you can give it no other argument than self. This is because arguments set during a specific tool instance’s initialization are hard to track, which prevents from sharing them properly to the hub. And anyway, the idea of making a specific class is that you can already set class attributes for anything you need to hard-code (just set your_variable=(...) directly under the class YourTool(Tool): line). And of course you can still create a class attribute anywhere in your code by assigning stuff to self.your_variable.

Once your tool is pushed to Hub, you can visualize it. Here is the model_downloads_tool that I’ve pushed. It has a nice gradio interface.

When diving into the tool files, you can find that all the tool’s logic is under tool.py. That is where you can inspect a tool shared by someone else.

Then you can load the tool with load_tool() or create it with from_hub() and pass it to the tools parameter in your agent. Since running tools means running custom code, you need to make sure you trust the repository, thus we require to pass trust_remote_code=True to load a tool from the Hub.

from smolagents import load_tool, CodeAgent

model_download_tool = load_tool(
    "{your_username}/hf-model-downloads",
    trust_remote_code=True
)

Import a Space as a tool

You can directly import a Space from the Hub as a tool using the Tool.from_space() method!

You only need to provide the id of the Space on the Hub, its name, and a description that will help you agent understand what the tool does. Under the hood, this will use gradio-client library to call the Space.

For instance, let’s import the FLUX.1-dev Space from the Hub and use it to generate an image.

image_generation_tool = Tool.from_space(
    "black-forest-labs/FLUX.1-schnell",
    name="image_generator",
    description="Generate an image from a prompt"
)

image_generation_tool("A sunny beach")

And voilà, here’s your image! 🏖️

Then you can use this tool just like any other tool. For example, let’s improve the prompt a rabbit wearing a space suit and generate an image of it.

from smolagents import CodeAgent, HfApiModel

model = HfApiModel("Qwen/Qwen2.5-Coder-32B-Instruct")
agent = CodeAgent(tools=[image_generation_tool], model=model)

agent.run(
    "Improve this prompt, then generate an image of it.", prompt='A rabbit wearing a space suit'
)

=== Agent thoughts:
improved_prompt could be "A bright blue space suit wearing rabbit, on the surface of the moon, under a bright orange sunset, with the Earth visible in the background"

Now that I have improved the prompt, I can use the image generator tool to generate an image based on this prompt.
>>> Agent is executing the code below:
image = image_generator(prompt="A bright blue space suit wearing rabbit, on the surface of the moon, under a bright orange sunset, with the Earth visible in the background")
final_answer(image)

How cool is this? 🤩

Use LangChain tools

We love Langchain and think it has a very compelling suite of tools. To import a tool from LangChain, use the from_langchain() method.

Here is how you can use it to recreate the intro’s search result using a LangChain web search tool. This tool will need pip install langchain google-search-results -q to work properly.

from langchain.agents import load_tools

search_tool = Tool.from_langchain(load_tools(["serpapi"])[0])

agent = CodeAgent(tools=[search_tool], model=model)

agent.run("How many more blocks (also denoted as layers) are in BERT base encoder compared to the encoder from the architecture proposed in Attention is All You Need?")

Manage your agent’s toolbox

You can manage an agent’s toolbox by adding or replacing a tool.

Let’s add the model_download_tool to an existing agent initialized with only the default toolbox.

from smolagents import HfApiModel

model = HfApiModel("Qwen/Qwen2.5-Coder-32B-Instruct")

agent = CodeAgent(tools=[], model=model, add_base_tools=True)
agent.toolbox.add_tool(model_download_tool)

Now we can leverage the new tool:

agent.run(
    "Can you give me the name of the model that has the most downloads in the 'text-to-video' task on the Hugging Face Hub but reverse the letters?"
)

Use the agent.toolbox.update_tool() method to replace an existing tool in the agent’s toolbox. This is useful if your new tool is a one-to-one replacement of the existing tool because the agent already knows how to perform that specific task. Just make sure the new tool follows the same API as the replaced tool or adapt the system prompt template to ensure all examples using the replaced tool are updated.

Use a collection of tools

You can leverage tool collections by using the ToolCollection object, with the slug of the collection you want to use. Then pass them as a list to initialize you agent, and start using them!

from transformers import ToolCollection, CodeAgent

image_tool_collection = ToolCollection(
    collection_slug="huggingface-tools/diffusion-tools-6630bb19a942c2306a2cdb6f",
    token="<YOUR_HUGGINGFACEHUB_API_TOKEN>"
)
agent = CodeAgent(tools=[*image_tool_collection.tools], model=model, add_base_tools=True)

agent.run("Please draw me a picture of rivers and lakes.")

To speed up the start, tools are loaded only if called by the agent.