> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/fastapi/fastapi/llms.txt
> Use this file to discover all available pages before exploring further.

# Cookie

> API reference for the FastAPI Cookie parameter function

# Cookie

Declare a cookie parameter for a path operation. Cookie parameters are extracted from HTTP request cookies.

```python theme={null}
from typing import Annotated
from fastapi import FastAPI, Cookie

app = FastAPI()

@app.get("/items/")
async def read_items(
    session_id: Annotated[str | None, Cookie()] = None
):
    return {"session_id": session_id}
```

## Signature

```python theme={null}
def Cookie(
    default: Any = Undefined,
    *,
    alias: str | None = None,
    title: str | None = None,
    description: str | None = None,
    gt: float | None = None,
    ge: float | None = None,
    lt: float | None = None,
    le: float | None = None,
    min_length: int | None = None,
    max_length: int | None = None,
    pattern: str | None = None,
    examples: list[Any] | None = None,
    deprecated: bool | str | None = None,
    include_in_schema: bool = True,
    json_schema_extra: dict[str, Any] | None = None,
) -> Any
```

## Parameters

<ParamField path="default" type="Any" default="Undefined">
  Default value if the parameter field is not set.
</ParamField>

<ParamField path="alias" type="str | None" default="None">
  An alternative name for the parameter field. This will be used to extract the data and for the generated OpenAPI.
</ParamField>

<ParamField path="title" type="str | None" default="None">
  Human-readable title for the parameter.
</ParamField>

<ParamField path="description" type="str | None" default="None">
  Human-readable description for the parameter.
</ParamField>

<ParamField path="gt" type="float | None" default="None">
  Greater than validation. If set, the value must be greater than this. Only applicable to numbers.
</ParamField>

<ParamField path="ge" type="float | None" default="None">
  Greater than or equal validation. If set, the value must be greater than or equal to this. Only applicable to numbers.
</ParamField>

<ParamField path="lt" type="float | None" default="None">
  Less than validation. If set, the value must be less than this. Only applicable to numbers.
</ParamField>

<ParamField path="le" type="float | None" default="None">
  Less than or equal validation. If set, the value must be less than or equal to this. Only applicable to numbers.
</ParamField>

<ParamField path="min_length" type="int | None" default="None">
  Minimum length for strings.
</ParamField>

<ParamField path="max_length" type="int | None" default="None">
  Maximum length for strings.
</ParamField>

<ParamField path="pattern" type="str | None" default="None">
  RegEx pattern for strings.
</ParamField>

<ParamField path="discriminator" type="str | None" default="None">
  Parameter field name for discriminating the type in a tagged union.
</ParamField>

<ParamField path="strict" type="bool | None" default="None">
  If True, strict validation is applied to the field.
</ParamField>

<ParamField path="multiple_of" type="float | None" default="None">
  Value must be a multiple of this. Only applicable to numbers.
</ParamField>

<ParamField path="allow_inf_nan" type="bool | None" default="None">
  Allow `inf`, `-inf`, `nan`. Only applicable to numbers.
</ParamField>

<ParamField path="max_digits" type="int | None" default="None">
  Maximum number of allowed digits for numbers.
</ParamField>

<ParamField path="decimal_places" type="int | None" default="None">
  Maximum number of decimal places allowed for numbers.
</ParamField>

<ParamField path="examples" type="list[Any] | None" default="None">
  Example values for this field.
</ParamField>

<ParamField path="deprecated" type="bool | str | None" default="None">
  Mark this parameter field as deprecated. It will affect the generated OpenAPI (visible at `/docs`).
</ParamField>

<ParamField path="include_in_schema" type="bool" default="True">
  Whether to include this parameter field in the generated OpenAPI.
</ParamField>

<ParamField path="json_schema_extra" type="dict[str, Any] | None" default="None">
  Any additional JSON schema data.
</ParamField>

## Examples

### Basic Cookie Parameter

```python theme={null}
from typing import Annotated
from fastapi import FastAPI, Cookie

app = FastAPI()

@app.get("/items/")
async def read_items(
    session_id: Annotated[str | None, Cookie()] = None
):
    return {"session_id": session_id}
```

### Required Cookie

```python theme={null}
@app.get("/items/")
async def read_items(
    session_id: Annotated[str, Cookie()]
):
    return {"session_id": session_id}
```

<Note>
  A cookie parameter is required when there is no default value.
</Note>

### Cookie with Validation

```python theme={null}
@app.get("/items/")
async def read_items(
    session_id: Annotated[str, Cookie(min_length=32, max_length=64)]
):
    return {"session_id": session_id}
```

### Multiple Cookies

```python theme={null}
@app.get("/items/")
async def read_items(
    session_id: Annotated[str | None, Cookie()] = None,
    tracking_id: Annotated[str | None, Cookie()] = None
):
    return {
        "session_id": session_id,
        "tracking_id": tracking_id
    }
```

### Cookie with Metadata

```python theme={null}
@app.get("/items/")
async def read_items(
    session_id: Annotated[
        str | None,
        Cookie(
            title="Session ID",
            description="The session identifier cookie"
        )
    ] = None
):
    return {"session_id": session_id}
```

## Common Use Cases

### Session Management

```python theme={null}
@app.get("/user/profile")
async def get_profile(
    session_token: Annotated[str, Cookie()]
):
    # Validate session and return user profile
    return {"session": session_token}
```

### Authentication Cookies

```python theme={null}
@app.get("/dashboard")
async def dashboard(
    access_token: Annotated[str | None, Cookie()] = None,
    refresh_token: Annotated[str | None, Cookie()] = None
):
    return {
        "access_token": access_token,
        "refresh_token": refresh_token
    }
```

### Tracking and Analytics

```python theme={null}
@app.get("/")
async def root(
    analytics_id: Annotated[str | None, Cookie()] = None,
    user_preferences: Annotated[str | None, Cookie()] = None
):
    return {
        "analytics_id": analytics_id,
        "preferences": user_preferences
    }
```

### CSRF Token

```python theme={null}
@app.post("/submit")
async def submit_form(
    csrf_token: Annotated[str, Cookie()]
):
    # Validate CSRF token
    return {"csrf_token": csrf_token}
```

<Note>
  Cookie parameters are read-only. To set cookies in the response, use the `Response` object or return a custom `Response`.
</Note>

## Setting Cookies in Response

```python theme={null}
from fastapi import Response

@app.post("/login")
async def login(response: Response):
    response.set_cookie(key="session_id", value="abc123")
    return {"message": "Logged in"}
```

<Warning>
  The `Cookie()` parameter function is only for reading cookies from requests. Use `response.set_cookie()` to set cookies in responses.
</Warning>