Response classes

Overview

FastrAPI provides several response classes for returning different content types from your route handlers. By default, routes return JSON, but you can use specific response classes for HTML, plain text, or redirects.

from fastrapi import FastrAPI
from fastrapi.responses import HTMLResponse, PlainTextResponse

app = FastrAPI()

@app.get("/html")
def get_html():
    return HTMLResponse("<h1>Hello World</h1>")

@app.get("/text")
def get_text():
    return PlainTextResponse("Hello World")

JSONResponse

Return JSON data with proper content-type headers.

from fastrapi.responses import JSONResponse

@app.get("/data")
def get_data():
    return JSONResponse(
        {"message": "Success", "data": [1, 2, 3]},
        status_code=200
    )

Constructor

content

dict | list | Any

required

The data to serialize as JSON. Can be any JSON-serializable Python object

status_code

int

default:"200"

The HTTP status code for the response

Properties

content

Any

The JSON content to be serialized

status_code

int

The HTTP status code

HTMLResponse

Return HTML content with text/html content-type.

from fastrapi.responses import HTMLResponse

@app.get("/page")
def get_page():
    html_content = """
    <!DOCTYPE html>
    <html>
        <head><title>My Page</title></head>
        <body>
            <h1>Welcome</h1>
            <p>This is an HTML response</p>
        </body>
    </html>
    """
    return HTMLResponse(html_content)

@app.get("/error")
def error_page():
    return HTMLResponse(
        "<h1>404 Not Found</h1>",
        status_code=404
    )

Constructor

content

str

required

The HTML content as a string

status_code

int

default:"200"

The HTTP status code for the response

Properties

content

str

The HTML content string

status_code

int

The HTTP status code

PlainTextResponse

Return plain text content with text/plain content-type.

from fastrapi.responses import PlainTextResponse

@app.get("/robots.txt")
def robots():
    content = """
    User-agent: *
    Disallow: /admin/
    Allow: /
    """
    return PlainTextResponse(content)

@app.get("/status")
def status():
    return PlainTextResponse("OK", status_code=200)

Constructor

content

str

required

The plain text content as a string

status_code

int

default:"200"

The HTTP status code for the response

Properties

content

str

The plain text content string

status_code

int

The HTTP status code

RedirectResponse

Return a redirect response with a Location header.

from fastrapi.responses import RedirectResponse

@app.get("/old-path")
def old_path():
    return RedirectResponse("/new-path")

@app.get("/external")
def external_redirect():
    return RedirectResponse(
        "https://example.com",
        status_code=302
    )

@app.post("/login")
def login(credentials):
    # Perform login logic
    return RedirectResponse("/dashboard", status_code=303)

Constructor

url

str

required

The URL to redirect to. Can be relative or absolute

status_code

int

default:"307"

The HTTP redirect status code. Common values:

301: Permanent redirect
302: Temporary redirect (changes method to GET)
303: See Other (always changes method to GET)
307: Temporary redirect (preserves method)
308: Permanent redirect (preserves method)

Properties

url

str

The redirect URL

status_code

int

The HTTP redirect status code

Status codes

All response classes accept a status_code parameter. Common HTTP status codes: Success (2xx)

200: OK
201: Created
202: Accepted
204: No Content

Redirection (3xx)

301: Moved Permanently
302: Found
303: See Other
307: Temporary Redirect
308: Permanent Redirect

Client Errors (4xx)

400: Bad Request
401: Unauthorized
403: Forbidden
404: Not Found
422: Unprocessable Entity

Server Errors (5xx)

500: Internal Server Error
502: Bad Gateway
503: Service Unavailable

Complete example

from fastrapi import FastrAPI
from fastrapi.responses import (
    JSONResponse,
    HTMLResponse,
    PlainTextResponse,
    RedirectResponse
)
from pydantic import BaseModel

app = FastrAPI()

class User(BaseModel):
    name: str
    email: str

@app.get("/")
def home():
    return HTMLResponse("""
        <!DOCTYPE html>
        <html>
            <head><title>Home</title></head>
            <body><h1>Welcome to FastrAPI</h1></body>
        </html>
    """)

@app.get("/api/users")
def list_users():
    return JSONResponse({
        "users": [
            {"id": 1, "name": "Alice"},
            {"id": 2, "name": "Bob"}
        ]
    })

@app.post("/api/users")
def create_user(user: User):
    return JSONResponse(
        {
            "id": 3,
            "name": user.name,
            "email": user.email,
            "created": True
        },
        status_code=201
    )

@app.get("/health")
def health_check():
    return PlainTextResponse("OK")

@app.get("/old-url")
def old_url():
    return RedirectResponse("/new-url", status_code=301)

@app.get("/robots.txt")
def robots():
    return PlainTextResponse(
        "User-agent: *\nAllow: /\n"
    )

@app.get("/download")
def download_file():
    # For custom headers, you can still use JSONResponse
    # with additional configuration
    return PlainTextResponse(
        "File content here",
        status_code=200
    )

if __name__ == "__main__":
    app.serve("127.0.0.1", 8080)

Default response type

By default, FastrAPI routes return JSONResponse when you return a dictionary or list:

@app.get("/data")
def get_data():
    # Automatically wrapped in JSONResponse
    return {"message": "Hello World"}

You can override the default response class in the FastrAPI constructor:

from fastrapi.responses import PlainTextResponse

app = FastrAPI(default_response_class=PlainTextResponse)

Core

Middleware

Advanced Features

Response classes

Overview