---
title: "ComponentTool"
id: componenttool
slug: "/componenttool"
description: "This wrapper allows using Haystack components to be used as tools by LLMs."
---

# ComponentTool

This wrapper allows using Haystack components to be used as tools by LLMs.

<div className="key-value-table">

|  |  |
| --- | --- |
| **Mandatory init variables** | `component`: The Haystack component to wrap                                         |
| **API reference**            | [ComponentTool](/reference/tools-api#componenttool)                       |
| **GitHub link**              | https://github.com/deepset-ai/haystack/blob/main/haystack/tools/component_tool.py |
| **Package name**             | `haystack-ai` |

</div>

## Overview

`ComponentTool` is a Tool that wraps Haystack components, allowing them to be used as tools by LLMs. ComponentTool automatically generates LLM-compatible tool schemas from component input sockets, which are derived from the component's `run` method signature and type hints.

It does input type conversion and offers support for components with run methods that have the following input types:

- Basic types (str, int, float, bool, dict)
- Dataclasses (both simple and nested structures)
- Lists of basic types (such as List[str])
- Lists of dataclasses (such as List[Document])
- Parameters with mixed types (such as List[Document], str...)

### Parameters

- `component` is mandatory and must be a Haystack component instance, either an existing one or a custom component.
- `name` is optional and defaults to the component class name in snake case, for example, "serper_dev_web_search" for `SerperDevWebSearch`.
- `description` is optional and defaults to the component’s docstring. This is what the LLM uses to decide when to call the tool.
- `parameters` is optional and lets you override the auto-generated JSON schema for the tool’s inputs.
- `outputs_to_string` is optional and controls how the component’s output is converted to a string for the LLM. By default, the full result dict is serialized. Use `{"source": "key"}` to extract a single output key, or add `"handler"` to apply a custom formatter. When wrapping an `Agent` as a sub-tool, use `{"source": "last_message"}` to surface only the agent’s final reply.
- `inputs_from_state` is optional and maps agent state keys to component input parameters. Example: `{"repository": "repo"}` passes the state value at `"repository"` as the component’s `"repo"` input.
- `outputs_to_state` is optional and maps component output keys to agent state keys. Example: `{"documents": {"source": "docs"}}` writes the component’s `"docs"` output to `"documents"` in state.

## Usage

:::tip
The recommended way to use `ComponentTool` in Haystack is with the [`Agent`](../pipeline-components/agents-1/agent.mdx) component, which manages the tool call loop for you. The pipeline example below shows the manual approach for cases where you need fine-grained control.
:::

### With the Agent Component

```python
from haystack.components.generators.chat import OpenAIChatGenerator
from haystack.dataclasses import ChatMessage
from haystack.tools import ComponentTool
from haystack.components.agents import Agent
from haystack.components.websearch import SerperDevWebSearch
from haystack.utils import Secret

# Create a SerperDev search component
search = SerperDevWebSearch(api_key=Secret.from_env_var("SERPERDEV_API_KEY"), top_k=3)

# Create a tool from the component
search_tool = ComponentTool(
    component=search,
    name="web_search",  # Optional: defaults to "serper_dev_web_search"
    description="Search the web for current information on any topic",  # Optional: defaults to component docstring
)

agent = Agent(
    system_prompt="You are an assistant that can use web search to find information.",
    chat_generator=OpenAIChatGenerator(),
    tools=[search_tool],
)

response = agent.run(
    messages=[ChatMessage.from_user("Give me a brief summary on who Nikola Tesla is")],
)

print(response["messages"][-1].text)
```

### In a Pipeline

You can also wire `ComponentTool` into a pipeline manually with `ChatGenerator` and `ToolInvoker` for full control over the tool call loop.

```python
from haystack import Pipeline
from haystack.tools import ComponentTool
from haystack.components.websearch import SerperDevWebSearch
from haystack.utils import Secret
from haystack.components.tools.tool_invoker import ToolInvoker
from haystack.components.generators.chat import OpenAIChatGenerator
from haystack.dataclasses import ChatMessage

# Create a SerperDev search component
search = SerperDevWebSearch(api_key=Secret.from_env_var("SERPERDEV_API_KEY"), top_k=3)

# Create a tool from the component
tool = ComponentTool(
    component=search,
    name="web_search",  # Optional: defaults to "serper_dev_web_search"
    description="Search the web for current information on any topic",  # Optional: defaults to component docstring
)

pipeline = Pipeline()
pipeline.add_component("llm", OpenAIChatGenerator(model="gpt-5.4-nano", tools=[tool]))
pipeline.add_component("tool_invoker", ToolInvoker(tools=[tool]))
pipeline.connect("llm.replies", "tool_invoker.messages")

message = ChatMessage.from_user(
    "Use the web search tool to find information about Nikola Tesla",
)

result = pipeline.run({"llm": {"messages": [message]}})

print(result)
```

## Additional References

📖 Related docs:

- [Multi-Agent Systems](../concepts/agents/multi-agent-systems.mdx)

📚 Tutorials:

- [Build a Tool-Calling Agent](https://haystack.deepset.ai/tutorials/43_building_a_tool_calling_agent)
- [Creating a Multi-Agent System with Haystack](https://haystack.deepset.ai/tutorials/45_creating_a_multi_agent_system)
