HTTP(s) Headers are key-value pairs that can be used by the client or the server to pass additional information along with an HTTP(s) request or response. An HTTP(s) header consists of its case-insensitive name followed by a colon (:), then by its value.
The ability to modify the headers of traffic that passes through your browser is a great tool to have. You can delete headers to minimize online tracking, remove CSP while testing, test sites in production and so on.
Using Requestly, Headers can be added/modified by a simple series of clicks. All you need is to install Requestly extension in your browser.
Modify Headers could be selected after clicking on New Rule button.
Select Modify Headers Rule
Select if you want to modify request header or response header and give a suitable name and description to the rule.