> ## Documentation Index
> Fetch the complete documentation index at: https://requestly-mintlify-changelog-requestly-past-week-38456.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# Modify Headers
> Modify HTTP request and response headers with Requestly for Free. Learn how to add, remove, or override headers for debugging, testing, and customizing API requests.
***
HTTP(s) Headers are key-value pairs that pass additional information with HTTP(s) requests or responses. This document explains how developers can use Requestly to modify these headers by adding, removing, or overriding values easily.
## Why Use the Modify Headers Rule
* **Open Websites in an iframe for Testing:** Headers like `X-Frame-Options` and `Content-Security-Policy` prevent pages from being opened in iframes to avoid clickjacking. Use Requestly to modify these headers for testing purposes.\
Learn more →
* **Remove Content-Security-Policy:** The `Content-Security-Policy` header restricts the injection of external scripts. Requestly can remove this header for testing purposes.\
Learn more →
* **Debugging CORS Issues:** To resolve CORS errors in browsers, modify response headers such as `Access-Control-Allow-Origin`, `Access-Control-Allow-Methods`, `Access-Control-Allow-Headers`, and `Access-Control-Allow-Credentials`.\
Learn more →
## Steps to Create Header Rules
Navigate to the **HTTP Rules** section and click on `+ New Rule` and select the `Modify Headers` option.
Provide a **descriptive name** for the rule to keep your setup organised. Optionally, add a brief **description** explaining its purpose for easier identification later.
Add conditions using **Source Condition** and **Source Filters** to target specific requests. Conditions can include URL, Host, or Path with matching options such as **Regex**, **Contains**, **Wildcard**, or **Equals**.
Let’s use an echo endpoint that returns request headers, body, query params etc as JSON response.\
Endpoint → `https://echo-http-requests.appspot.com/echo`
In this step, you can select the option to modify. It rule allows you to edit both the request and the response headers.
Specify key-value pairs to add, remove, or override headers. If you want to **Modify** **Request Headers**, add values under the Request headers tab.
Specify key-value pairs to add, remove, or override headers. If you want to **Modify Response headers**, add values under the Response headers tab.
Once you are satisfied with your configuration, click `Save` to store the rule. After saving, make sure to toggle the rule `ON` to activate it. This will apply the rule and ensure it works as expected.
There are multiple ways to validate if a rule is applied or not, learn more about how to [`validate rule execution`](/general/http-rules/advanced-usage/validate-rules-execution).
Test the rule by opening the URL \[[`https://echo-http-requests.appspot.com/echo`](https://echo-http-requests.appspot.com/echo)] in a new tab to see the changed header values.
Test by calling the API from Requestly’s API Client.
