tiangolo.fastapi/docs/tutorial/request-files.md

You can define files to be uploaded by the client using File.

Import File

Import File from fastapi:

{!./src/request_files/tutorial001.py!}

Define File parameters

Create file parameters the same way you would for Body or Form:

{!./src/request_files/tutorial001.py!}

The files will be uploaded as form data and you will receive the contents as bytes.

!!! info File is a class that inherits directly from Form.

!!! info To declare File bodies, you need to use File, because otherwise the parameters would be interpreted as query parameters or body (JSON) parameters.

"Form Data"?

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 when it doesn't include files.

But when the form includes files, it is encoded as `multipart/form-data`. If you use `File`, **FastAPI** will know it has to get the files from the correct part of the body.

If you want to read more about these encondings and form fields, head to the <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST" target="_blank"><abbr title="Mozilla Developer Network">MDN</abbr> web docs for <code>POST</code></a>.

!!! warning You can declare multiple File and 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 multipart/form-data instead of application/json.

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

Recap

Use File to declare files to be uploaded as input parameters (as form data).