# Parameter types for tool use (function calling)

> Guide on using structured outputs with tool parameters in the Cohere Chat API. Includes guide on supported parameter types and usage examples (API v2).

## Structured Outputs (Tools)

The [Structured Outputs](https://docs.cohere.com/docs/structured-outputs) feature guarantees that an LLM’s response will strictly follow a schema specified by the user.

While this feature is supported in two scenarios (JSON and tools), this page will focus on the tools scenario.

### Usage

When you use the Chat API with `tools`, setting the `strict_tools` parameter to `True` will guarantee that every generated tool call follows the specified tool schema.

Concretely, this means:

* No hallucinated tool names
* No hallucinated tool parameters
* Every `required` parameter is included in the tool call
* All parameters produce the requested data types

With `strict_tools` enabled, the API will ensure that the tool names and tool parameters are generated according to the tool definitions. This eliminates tool name and parameter hallucinations, ensures that each parameter matches the specified data type, and that all required parameters are included in the model response.

Additionally, this results in faster development. You don’t need to spend a lot of time prompt engineering the model to avoid hallucinations.

When the `strict_tools` parameter is set to `True`, you can define a maximum of 200 fields across all tools being passed to an API call.

```python PYTHON {4}
response = co.chat(model="command-a-03-2025",
    messages=[{"role": "user", "content": "What's the weather in Toronto?"}],
    tools=tools,
    strict_tools=True
)
```

### Important notes

When using `strict_tools`, the following notes apply:

* This parameter is only supported in Chat API V2 via the strict\_tools parameter (not API V1).
* You must specify at least one `required` parameter. Tools with only optional parameters are not supported in this mode.
* You can define a maximum of 200 fields across all tools in a single Chat API call.

## Supported parameter types

Structured Outputs supports a subset of the JSON Schema specification. Refer to the [Structured Outputs documentation](https://docs.cohere.com/docs/structured-outputs#parameter-types-support) for the list of supported and unsupported parameters.

## Usage examples

This section provides usage examples of the JSON Schema [parameters that are supported](https://docs.cohere.com/v2/docs/tool-use#structured-outputs-tools) in Structured Outputs (Tools).

<Accordion title="Helper code">
  The examples on this page each provide a tool schema and a `message` (the user message). To get an output, pass those values to a Chat endpoint call, as shown in the helper code below.

  <Tabs>
    <Tab title="Cohere platform">
      ```python PYTHON
      # ! pip install -U cohere
      import cohere

      co = cohere.ClientV2(
          "COHERE_API_KEY"
      )  # Get your free API key here: https://dashboard.cohere.com/api-keys
      ```
    </Tab>

    <Tab title="Private deployment">
      ```python PYTHON
      # ! pip install -U cohere
      import cohere

      co = cohere.ClientV2(
          api_key="",  # Leave this blank
          base_url="<YOUR_DEPLOYMENT_URL>",
      )
      ```
    </Tab>
  </Tabs>

  <CodeBlocks>
    ```python PYTHON
    response = co.chat(
        # The model name. Example: command-a-03-2025
        model="MODEL_NAME",
        # The user message. Optional - you can first add a `system_message` role
        messages=[
            {
                "role": "user",
                "content": message,
            }
        ],
        # The tool schema that you define
        tools=tools,
        # This guarantees that the output will adhere to the schema
        strict_tools=True,
        # Typically, you'll need a low temperature for more deterministic outputs
        temperature=0,
    )

    for tc in response.message.tool_calls:
        print(f"{tc.function.name} | Parameters: {tc.function.arguments}")
    ```

    ```bash cURL
    curl --request POST \
      --url https://api.cohere.ai/v2/chat \
      --header 'accept: application/json' \
      --header 'content-type: application/json' \
      --header "Authorization: bearer $CO_API_KEY" \
      --data '{
      "model": "command-a-03-2025",
      "messages": [
        {
          "role": "user",
          "content": "What'\''s the weather in Toronto?"
        }
      ],
      "tools": [
        {
          "type": "function",
          "function": {
            "name": "get_weather",
            "description": "Gets the weather of a given location",
            "parameters": {
              "type": "object",
              "properties": {
                "location": {
                  "type": "string",
                  "description": "the location to get the weather, example: San Francisco."
                }
              },
              "required": ["location"]
            }
          }
        }
      ],
      "strict_tools": true,
      "temperature": 0
    }'
    ```
  </CodeBlocks>
</Accordion>

### Basic types

#### String

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "get_weather",
            "description": "Gets the weather of a given location",
            "parameters": {
                "type": "object",
                "properties": {
                    "location": {
                        "type": "string",
                        "description": "the location to get the weather, example: San Francisco.",
                    }
                },
                "required": ["location"],
            },
        },
    },
]

message = "What's the weather in Toronto?"
```

Example response:

```mdx wordWrap
get_weather
{
  "location": "Toronto"
}
```

#### Integer

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "add_numbers",
            "description": "Adds two numbers",
            "parameters": {
                "type": "object",
                "properties": {
                    "first_number": {
                        "type": "integer",
                        "description": "The first number to add.",
                    },
                    "second_number": {
                        "type": "integer",
                        "description": "The second number to add.",
                    },
                },
                "required": ["first_number", "second_number"],
            },
        },
    }
]

message = "What is five plus two"
```

Example response:

```mdx wordWrap
add_numbers
{
  "first_number": 5,
  "second_number": 2
}
```

#### Float

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "add_numbers",
            "description": "Adds two numbers",
            "parameters": {
                "type": "object",
                "properties": {
                    "first_number": {
                        "type": "number",
                        "description": "The first number to add.",
                    },
                    "second_number": {
                        "type": "number",
                        "description": "The second number to add.",
                    },
                },
                "required": ["first_number", "second_number"],
            },
        },
    }
]

message = "What is 5.3 plus 2"
```

Example response:

```mdx wordWrap
add_numbers
{
  "first_number": 5.3,
  "second_number": 2
}
```

#### Boolean

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "reserve_tickets",
            "description": "Reserves a train ticket",
            "parameters": {
                "type": "object",
                "properties": {
                    "quantity": {
                        "type": "integer",
                        "description": "The quantity of tickets to reserve.",
                    },
                    "trip_protection": {
                        "type": "boolean",
                        "description": "Indicates whether to add trip protection.",
                    },
                },
                "required": ["quantity", "trip_protection"],
            },
        },
    }
]

message = "Book me 2 tickets. I don't need trip protection."
```

Example response:

```mdx wordWrap
reserve_tickets
{
  "quantity": 2,
  "trip_protection": false
}
```

### Array

#### With specific types

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "get_weather",
            "description": "Gets the weather of a given location",
            "parameters": {
                "type": "object",
                "properties": {
                    "locations": {
                        "type": "array",
                        "items": {"type": "string"},
                        "description": "The locations to get weather.",
                    }
                },
                "required": ["locations"],
            },
        },
    },
]

message = "What's the weather in Toronto and New York?"
```

Example response:

```mdx wordWrap
get_weather
{
  "locations": [
    "Toronto",
    "New York"
  ]
}
```

#### Without specific types

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "get_weather",
            "description": "Gets the weather of a given location",
            "parameters": {
                "type": "object",
                "properties": {
                    "locations": {
                        "type": "array",
                        "description": "The locations to get weather.",
                    }
                },
                "required": ["locations"],
            },
        },
    },
]

message = "What's the weather in Toronto and New York?"
```

Example response:

```mdx wordWrap
get_weather
{
  "locations": [
    "Toronto",
    "New York"
  ]
}
```

#### Lists of lists

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "maxPoints",
            "description": "Finds the maximum number of points on a line.",
            "parameters": {
                "type": "object",
                "properties": {
                    "points": {
                        "type": "array",
                        "description": "The list of points. Points are 2 element lists [x, y].",
                        "items": {
                            "type": "array",
                            "items": {"type": "integer"},
                            "description": "A point represented by a 2 element list [x, y].",
                        },
                    }
                },
                "required": ["points"],
            },
        },
    }
]

message = "Please provide the maximum number of collinear points for this set of coordinates - [[1,1],[2,2],[3,4],[5,5]]."
```

Example response:

```mdx wordWrap
maxPoints
{
  "points": [
    [1,1],
    [2,2],
    [3,4],
    [5,5]
  ]
}
```

### Others

#### Nested objects

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "search_furniture_products",
            "description": "Searches for furniture products given the user criteria.",
            "parameters": {
                "type": "object",
                "properties": {
                    "product_type": {
                        "type": "string",
                        "description": "The type of the product to search for.",
                    },
                    "features": {
                        "type": "object",
                        "properties": {
                            "material": {"type": "string"},
                            "style": {"type": "string"},
                        },
                        "required": ["style"],
                    },
                },
                "required": ["product_type"],
            },
        },
    }
]

message = "I'm looking for a dining table made of oak in Scandinavian style."
```

Example response:

```mdx wordWrap
search_furniture_products
{
  "features": {
    "material": "oak",
    "style": "Scandinavian"
  },
  "product_type": "dining table"
}
```

#### Enums

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "fetch_contacts",
            "description": "Fetch a contact by type",
            "parameters": {
                "type": "object",
                "properties": {
                    "contact_type": {
                        "type": "string",
                        "description": "The type of contact to fetch.",
                        "enum": ["customer", "supplier"],
                    }
                },
                "required": ["contact_type"],
            },
        },
    }
]

message = "Give me vendor contacts."
```

Example response:

```mdx wordWrap
fetch_contacts
{
  "contact_type": "supplier"
}
```

#### Const

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "get_weather",
            "description": "Gets the weather of a given location",
            "parameters": {
                "type": "object",
                "properties": {
                    "location": {
                        "type": "string",
                        "description": "The location to get weather.",
                    },
                    "country": {
                        "type": "string",
                        "description": "The country for the weather lookup",
                        "const": "Canada",
                    },
                },
                "required": ["location", "country"],
            },
        },
    },
]

message = "What's the weather in Toronto and Vancouver?"
```

Example response:

```mdx wordWrap
get_weather
{
  "country": "Canada",
  "location": "Toronto"
}
---
get_weather
{
  "country": "Canada",
  "location": "Vancouver"
}
---
```

#### Pattern

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "query_product_by_sku",
            "description": "Queries products by SKU pattern",
            "parameters": {
                "type": "object",
                "properties": {
                    "sku_pattern": {
                        "type": "string",
                        "description": "Pattern to match SKUs",
                        "pattern": "[A-Z]{3}[0-9]{4}",
                    }
                },
                "required": ["sku_pattern"],
            },
        },
    }
]

message = "Check the stock level of this product - 7374 hgY"
```

Example response:

```mdx wordWrap
query_product_by_sku
{
  "sku_pattern": "HGY7374"
}
```

#### Format

```python PYTHON
tools = [
    {
        "type": "function",
        "function": {
            "name": "book_hotel",
            "description": "Books a hotel room for a specific check-in date",
            "parameters": {
                "type": "object",
                "properties": {
                    "hotel_name": {
                        "type": "string",
                        "description": "Name of the hotel",
                    },
                    "check_in_date": {
                        "type": "string",
                        "description": "Check-in date for the hotel",
                        "format": "date",
                    },
                },
                "required": ["hotel_name", "check_in_date"],
            },
        },
    }
]

message = "Book a room at the Grand Hotel with check-in on Dec 2 2024"
```

Example response:

```mdx wordWrap
book_hotel
{
  "check_in_date": "2024-12-02",
  "hotel_name": "Grand Hotel"
}
```