# Custom Response - HTML, Stream, File, others
By default, **FastAPI** will return JSON responses.
You can override it by returning a `Response` directly as seen in [Return a Response directly](/guides/advanced-user-guide-response-directly).
But if you return a `Response` directly (or any subclass, like `JSONResponse`), the data won't be automatically converted (even if you declare a `response_model`), and the documentation won't be automatically generated (for example, including the specific "media type", in the HTTP header `Content-Type` as part of the generated OpenAPI).
But you can also declare the `Response` that you want to be used (e.g. any `Response` subclass), in the _path operation decorator_ using the `response_class` parameter.
The contents that you return from your _path operation function_ will be put inside of that `Response`.
:::callout{intent="note"}
If you use a response class with no media type, FastAPI will expect your response to have no content, so it will not document the response format in its generated OpenAPI docs.
:::
## JSON Responses
By default FastAPI returns JSON responses.
If you declare a [Response Model](/guides/tutorial-user-guide-response-model) FastAPI will use it to serialize the data to JSON, using Pydantic.
If you don't declare a response model, FastAPI will use the `jsonable_encoder` explained in [JSON Compatible Encoder](/guides/tutorial-user-guide-encoder) and put it in a `JSONResponse`.
If you declare a `response_class` with a JSON media type (`application/json`), like is the case with the `JSONResponse`, the data you return will be automatically converted (and filtered) with any Pydantic `response_model` that you declared in the _path operation decorator_. But the data won't be serialized to JSON bytes with Pydantic, instead it will be converted with the `jsonable_encoder` and then passed to the `JSONResponse` class, which will serialize it to bytes using the standard JSON library in Python.
### JSON Performance
In short, if you want the maximum performance, use a [Response Model](/guides/tutorial-user-guide-response-model) and don't declare a `response_class` in the _path operation decorator_.
```python
from fastapi import FastAPI
from pydantic import BaseModel
app = FastAPI()
class Item(BaseModel):
name: str
description: str | None = None
price: float
tax: float | None = None
tags: list[str] = []
@app.post("/items/")
async def create_item(item: Item) -> Item:
return item
@app.get("/items/")
async def read_items() -> list[Item]:
return [
Item(name="Portal Gun", price=42.0),
Item(name="Plumbus", price=32.0),
]
```
## HTML Response
To return a response with HTML directly from **FastAPI**, use `HTMLResponse`.
- Import `HTMLResponse`.
- Pass `HTMLResponse` as the parameter `response_class` of your _path operation decorator_.
```python
from fastapi import FastAPI
from fastapi.responses import HTMLResponse
app = FastAPI()
@app.get("/items/", response_class=HTMLResponse)
async def read_items():
return """
Some HTML in here
Look ma! HTML!
"""
```
:::callout{intent="note"}
The parameter `response_class` will also be used to define the "media type" of the response.
In this case, the HTTP header `Content-Type` will be set to `text/html`.
And it will be documented as such in OpenAPI.
:::
### Return a `Response`
As seen in [Return a Response directly](/guides/advanced-user-guide-response-directly), you can also override the response directly in your _path operation_, by returning it.
The same example from above, returning an `HTMLResponse`, could look like:
```python
from fastapi import FastAPI
from fastapi.responses import HTMLResponse
app = FastAPI()
@app.get("/items/")
async def read_items():
html_content = """
Some HTML in here
Look ma! HTML!
"""
return HTMLResponse(content=html_content, status_code=200)
```
:::callout{intent="warning"}
A `Response` returned directly by your _path operation function_ won't be documented in OpenAPI (for example, the `Content-Type` won't be documented) and won't be visible in the automatic interactive docs.
:::
:::callout{intent="note"}
Of course, the actual `Content-Type` header, status code, etc, will come from the `Response` object you returned.
:::
### Document in OpenAPI and override `Response`
If you want to override the response from inside of the function but at the same time document the "media type" in OpenAPI, you can use the `response_class` parameter AND return a `Response` object.
The `response_class` will then be used only to document the OpenAPI _path operation_, but your `Response` will be used as is.
#### Return an `HTMLResponse` directly
For example, it could be something like:
```python
from fastapi import FastAPI
from fastapi.responses import HTMLResponse
app = FastAPI()
def generate_html_response():
html_content = """
Some HTML in here
Look ma! HTML!
"""
return HTMLResponse(content=html_content, status_code=200)
@app.get("/items/", response_class=HTMLResponse)
async def read_items():
return generate_html_response()
```
In this example, the function `generate_html_response()` already generates and returns a `Response` instead of returning the HTML in a `str`.
By returning the result of calling `generate_html_response()`, you are already returning a `Response` that will override the default **FastAPI** behavior.
But as you passed the `HTMLResponse` in the `response_class` too, **FastAPI** will know how to document it in OpenAPI and the interactive docs as HTML with `text/html`:
## Available responses
Here are some of the available responses.
Keep in mind that you can use `Response` to return anything else, or even create a custom sub-class.
:::callout{intent="note" title="Technical Details"}
You could also use `from starlette.responses import HTMLResponse`.
**FastAPI** provides the same `starlette.responses` as `fastapi.responses` just as a convenience for you, the developer. But most of the available responses come directly from Starlette.
:::
### `Response`
The main `Response` class, all the other responses inherit from it.
You can return it directly.
It accepts the following parameters:
- `content` - A `str` or `bytes`.
- `status_code` - An `int` HTTP status code.
- `headers` - A `dict` of strings.
- `media_type` - A `str` giving the media type. E.g. `"text/html"`.
FastAPI (actually Starlette) will automatically include a Content-Length header. It will also include a Content-Type header, based on the `media_type` and appending a charset for text types.
```python
from fastapi import FastAPI, Response
app = FastAPI()
@app.get("/legacy/")
def get_legacy_data():
data = """
You'll have to use soap here.
"""
return Response(content=data, media_type="application/xml")
```
### `HTMLResponse`
Takes some text or bytes and returns an HTML response, as you read above.
### `PlainTextResponse`
Takes some text or bytes and returns a plain text response.
```python
from fastapi import FastAPI
from fastapi.responses import PlainTextResponse
app = FastAPI()
@app.get("/", response_class=PlainTextResponse)
async def main():
return "Hello World"
```
### `JSONResponse`
Takes some data and returns an `application/json` encoded response.
This is the default response used in **FastAPI**, as you read above.
:::callout{intent="note" title="Technical Details"}
But if you declare a response model or return type, that will be used directly to serialize the data to JSON, and a response with the right media type for JSON will be returned directly, without using the `JSONResponse` class.
This is the ideal way to get the best performance.
:::
### `RedirectResponse`
Returns an HTTP redirect. Uses a 307 status code (Temporary Redirect) by default.
You can return a `RedirectResponse` directly:
```python
from fastapi import FastAPI
from fastapi.responses import RedirectResponse
app = FastAPI()
@app.get("/typer")
async def redirect_typer():
return RedirectResponse("https://typer.tiangolo.com")
```
***
Or you can use it in the `response_class` parameter:
```python
from fastapi import FastAPI
from fastapi.responses import RedirectResponse
app = FastAPI()
@app.get("/fastapi", response_class=RedirectResponse)
async def redirect_fastapi():
return "https://fastapi.tiangolo.com"
```
If you do that, then you can return the URL directly from your _path operation_ function.
In this case, the `status_code` used will be the default one for the `RedirectResponse`, which is `307`.
***
You can also use the `status_code` parameter combined with the `response_class` parameter:
```python
from fastapi import FastAPI
from fastapi.responses import RedirectResponse
app = FastAPI()
@app.get("/pydantic", response_class=RedirectResponse, status_code=302)
async def redirect_pydantic():
return "https://docs.pydantic.dev/"
```
### `StreamingResponse`
Takes an async generator or a normal generator/iterator (a function with `yield`) and streams the response body.
```python
import anyio
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
app = FastAPI()
async def fake_video_streamer():
for i in range(10):
yield b"some fake video bytes"
await anyio.sleep(0)
@app.get("/")
async def main():
return StreamingResponse(fake_video_streamer())
```
:::callout{intent="note" title="Technical Details"}
An `async` task can only be cancelled when it reaches an `await`. If there is no `await`, the generator (function with `yield`) can not be cancelled properly and may keep running even after cancellation is requested.
Since this small example does not need any `await` statements, we add an `await anyio.sleep(0)` to give the event loop a chance to handle cancellation.
This would be even more important with large or infinite streams.
:::
:::callout{intent="tip"}
Instead of returning a `StreamingResponse` directly, you should probably follow the style in [Stream Data](/guides/advanced-user-guide-stream-data), it's much more convenient and handles cancellation behind the scenes for you.
If you are streaming JSON Lines, follow the [Stream JSON Lines](/guides/tutorial-user-guide-stream-json-lines) tutorial.
:::
### `FileResponse`
Asynchronously streams a file as the response.
Takes a different set of arguments to instantiate than the other response types:
- `path` - The file path to the file to stream.
- `headers` - Any custom headers to include, as a dictionary.
- `media_type` - A string giving the media type. If unset, the filename or path will be used to infer a media type.
- `filename` - If set, this will be included in the response `Content-Disposition`.
File responses will include appropriate `Content-Length`, `Last-Modified` and `ETag` headers.
```python
from fastapi import FastAPI
from fastapi.responses import FileResponse
some_file_path = "large-video-file.mp4"
app = FastAPI()
@app.get("/")
async def main():
return FileResponse(some_file_path)
```
You can also use the `response_class` parameter:
```python
from fastapi import FastAPI
from fastapi.responses import FileResponse
some_file_path = "large-video-file.mp4"
app = FastAPI()
@app.get("/", response_class=FileResponse)
async def main():
return some_file_path
```
In this case, you can return the file path directly from your _path operation_ function.
## Custom response class
You can create your own custom response class, inheriting from `Response` and using it.
For example, let's say that you want to use [`orjson`](https://github.com/ijl/orjson) with some settings.
Let's say you want it to return indented and formatted JSON, so you want to use the orjson option `orjson.OPT_INDENT_2`.
You could create a `CustomORJSONResponse`. The main thing you have to do is create a `Response.render(content)` method that returns the content as `bytes`:
```python
from typing import Any
import orjson
from fastapi import FastAPI, Response
app = FastAPI()
class CustomORJSONResponse(Response):
media_type = "application/json"
def render(self, content: Any) -> bytes:
assert orjson is not None, "orjson must be installed"
return orjson.dumps(content, option=orjson.OPT_INDENT_2)
@app.get("/", response_class=CustomORJSONResponse)
async def main():
return {"message": "Hello World"}
```
Now instead of returning:
```json
{"message": "Hello World"}
```
...this response will return:
```json
{
"message": "Hello World"
}
```
Of course, you will probably find much better ways to take advantage of this than formatting JSON. 😉
### `orjson` or Response Model
If what you are looking for is performance, you are probably better off using a [Response Model](/guides/tutorial-user-guide-response-model) than an `orjson` response.
With a response model, FastAPI will use Pydantic to serialize the data to JSON, without using intermediate steps, like converting it with `jsonable_encoder`, which would happen in any other case.
And under the hood, Pydantic uses the same underlying Rust mechanisms as `orjson` to serialize to JSON, so you will already get the best performance with a response model.
## Default response class
When creating a **FastAPI** class instance or an `APIRouter` you can specify which response class to use by default.
The parameter that defines this is `default_response_class`.
In the example below, **FastAPI** will use `HTMLResponse` by default, in all _path operations_, instead of JSON.
```python
from fastapi import FastAPI
from fastapi.responses import HTMLResponse
app = FastAPI(default_response_class=HTMLResponse)
@app.get("/items/")
async def read_items():
return "Items
This is a list of items.
"
```
:::callout{intent="tip"}
You can still override `response_class` in _path operations_ as before.
:::
## Additional documentation
You can also declare the media type and many other details in OpenAPI using `responses`: [Additional Responses in OpenAPI](/guides/advanced-user-guide-additional-responses).
## Related pages
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