fastapi__fastapi/docs/tutorial/request-forms.md

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

!!! info
    To use forms, first install <a href="https://andrew-d.github.io/python-multipart/" class="external-link" target="_blank">`python-multipart`</a>.

    E.g. `pip install python-multipart`.

## Import `Form`

Import `Form` from `fastapi`:

```Python hl_lines="1"
{!./src/request_forms/tutorial001.py!}
```

## Define `Form` parameters

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

```Python hl_lines="7"
{!./src/request_forms/tutorial001.py!}
```

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 <abbr title="specification">spec</abbr> 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 metadata and validation as with `Body` (and `Query`, `Path`, `Cookie`).

!!! info
    `Form` is a class that inherits directly from `Body`.

!!! 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>`) sends 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.

!!! note "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 <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST" class="external-link" target="_blank"><abbr title="Mozilla Developer Network">MDN</abbr> web docs for <code>POST</code></a>.

!!! 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.