> ## 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.

# UploadFile

> A file uploaded in a request with async-compatible methods for reading and writing.

## UploadFile

A file uploaded in a request. Define it as a path operation function parameter or dependency to receive uploaded files.

For regular `def` functions, you can use the `upload_file.file` attribute to access the raw standard Python file (blocking, not async).

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

app = FastAPI()

@app.post("/files/")
async def create_file(file: Annotated[bytes, File()]):
    return {"file_size": len(file)}

@app.post("/uploadfile/")
async def create_upload_file(file: UploadFile):
    return {"filename": file.filename}
```

## Attributes

<ParamField path="file" type="BinaryIO">
  The standard Python file object (non-async). Useful for non-async code.
</ParamField>

<ParamField path="filename" type="str | None">
  The original file name sent by the client.
</ParamField>

<ParamField path="size" type="int | None">
  The size of the file in bytes.
</ParamField>

<ParamField path="headers" type="Headers">
  The headers of the request.
</ParamField>

<ParamField path="content_type" type="str | None">
  The content type of the file from the request headers (e.g., "image/png", "application/pdf").
</ParamField>

## Methods

### read

Read bytes from the file asynchronously.

```python theme={null}
async def read(size: int = -1) -> bytes
```

<ParamField path="size" type="int" default="-1">
  The number of bytes to read from the file. Default is -1, which reads the entire file.
</ParamField>

**Returns:** The bytes read from the file.

### write

Write bytes to the file asynchronously.

```python theme={null}
async def write(data: bytes) -> None
```

<ParamField path="data" type="bytes" required>
  The bytes to write to the file.
</ParamField>

Note: You normally wouldn't use this method for files received in a request.

### seek

Move to a specific position in the file.

```python theme={null}
async def seek(offset: int) -> None
```

<ParamField path="offset" type="int" required>
  The position in bytes to seek to in the file.
</ParamField>

Any subsequent read or write will start from this position.

### close

Close the file.

```python theme={null}
async def close() -> None
```

Always close files when you're done to free up system resources.

## Usage Notes

* All methods are async-compatible and run in a threadpool
* The file is automatically stored in memory up to a size limit, then spooled to disk
* For small files, content is kept in memory for better performance
* Use `await file.read()` to read the entire file contents
* Remember to `await file.close()` or use context managers when appropriate

## Learn More

Read more in the [FastAPI docs for Request Files](https://fastapi.tiangolo.com/tutorial/request-files/).