What is a Header Parameter?

Headers are pieces of information that are transmitted with the request and received with the response. So we can manipulate both in Fast API.

1. Request Headers: HTTP request is used in HTTP requests, but it is not related to the content of the message.
2. Response Headers: HTTP request is used in HTTP response, but it is not related to the content of the message.

So first of all, in Python, we can add a specific custom header to our function definition. Or actually, if we want an existing header, we can do that too. Just make sure it’s not one of those headers that are automatically written or overwritten by the request if we make the request to the browser.

To use header parameters in FastAPI, use the Header() decorator. The decorator allows a parameter to be declared as a header parameter.

Adding headers in the request function definition:

from fastapi import FastAPI, Header

@app.get(“/”)

def root(custom_header: Optional[str] = Header(None)):

…

Note: Provide default value as header from FastAPI. Otherwise, it will be interpreted as a query parameter. The Optional[str], header type informs FastAPI that the custom_header parameter is optional. and Header(None)) tell the system that we are expecting a header for this parameter.

Note: We can attach as many headers as we want here to the response.

FastAPI is the fastest-growing Python API development framework, It is easy to lightweight, and user-friendly and It is based on standard Python-type hints, which makes it easier to use and understand.

FastAPI supports header parameters, these are used to validate and process incoming API calls. In this article, you will learn everything you need to know about header parameters in FastAPI, request headers and response headers, how to add headers to the request function definition, how to provide custom response headers and explain with the help of examples. Lastly, the benefits of using header parameters. At the end of this article, you will have a solid understanding of header parameters, and how to implement them to set up a robust and secure REST API.