HookAjax is a free Chrome extension developed by Kenny Huang that allows users to modify the response text of Fetch or XHR requests. Whether you want to test different scenarios or debug your code, this extension provides a convenient way to manipulate the data returned by these requests.

To get started with HookAjax, you may need to restart your Chrome browser after adding the extension. It is also recommended to turn off the extension when you're not using it to avoid any unintended effects on your browsing experience.

One important thing to note is that HookAjax only overrides the response data in the XMLHTTPRequest object and the fetch method. The "real" response that you can see in Chrome's DevTools' "Network" panel will not be changed. This means that the modifications made with HookAjax are limited to the JavaScript layer and will only affect how the data is presented on the page.

Overall, HookAjax is a useful tool for developers who need to manipulate Fetch or XHR requests in their web applications. With its easy-to-use interface and ability to modify response texts, it provides a convenient way to test and debug your code.