# Form Data

When you need to receive form fields instead of JSON, you can use `Form`.

:::callout{intent="note"}
To use forms, first install [`python-multipart`](https://github.com/Kludex/python-multipart).

Add it to your project:

```console
$ uv add python-multipart
```
:::

## Import `Form`

Import `Form` from `fastapi`:

```python
from typing import Annotated

from fastapi import FastAPI, Form

app = FastAPI()


@app.post("/login/")
async def login(username: Annotated[str, Form()], password: Annotated[str, Form()]):
    return {"username": username}
```

## Define `Form` parameters

Create form parameters the same way you would for `Body` or `Query`:

```python
from typing import Annotated

from fastapi import FastAPI, Form

app = FastAPI()


@app.post("/login/")
async def login(username: Annotated[str, Form()], password: Annotated[str, Form()]):
    return {"username": username}
```

For example, in one of the ways the OAuth2 specification can be used (called "password flow") it is required to send a `username` and `password` as form fields.

The spec requires the fields to be exactly named `username` and `password`, and to be sent as form fields, not JSON.

With `Form` you can declare the same configurations as with `Body` (and `Query`, `Path`, `Cookie`), including validation, examples, an alias (e.g. `user-name` instead of `username`), etc.

:::callout{intent="note"}
`Form` is a class that inherits directly from `Body`.
:::

:::callout{intent="tip"}
To declare form bodies, you need to use `Form` explicitly, because without it the parameters would be interpreted as query parameters or body (JSON) parameters.
:::

## About "Form Fields"

The way HTML forms (`<form></form>`) send the data to the server normally uses a "special" encoding for that data, it's different from JSON.

**FastAPI** will make sure to read that data from the right place instead of JSON.

:::callout{intent="note" title="Technical Details"}
Data from forms is normally encoded using the "media type" `application/x-www-form-urlencoded`.

But when the form includes files, it is encoded as `multipart/form-data`. You'll read about handling files in the next chapter.

If you want to read more about these encodings and form fields, head to the [MDN (Mozilla Developer Network) web docs for `POST`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST).
:::

:::callout{intent="warning"}
You can declare multiple `Form` parameters in a _path operation_, but you can't also declare `Body` fields that you expect to receive as JSON, as the request will have the body encoded using `application/x-www-form-urlencoded` instead of `application/json`.

This is not a limitation of **FastAPI**, it's part of the HTTP protocol.
:::

## Recap

Use `Form` to declare form data input parameters.

## Related pages

- [About](./about-index.md)
- [Advanced User Guide](./advanced-user-guide-index.md)
- [Deployment](./deployment-index.md)
- [FastAPI](./fastapi-index.md)
- [FastAPI Docs](../index.md)
- [Features](./features-index.md)
- [How To - Recipes](./how-to-recipes-index.md)
- [Learn](./learn-index.md)
- [More](./more-index.md)
- [OpenAPI](./openapi-index.md)

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