Our team thought of this while working on a project whose backend api's timelines were way different. While building the UI, we had to use mock responses in the code which made it really messy.
This chrome extension speeds up not only the development process of frontend, but also useful to test different UAT cases on staging, QA or even production environment.
Frontend project is kept clean with real api integration.
The extension take care of aborting the network call for configured api, and provide custom response.
UI is very clean and easy to understand even for beginners.
It will be great if you can add import/export features in the extension so that stubs can be shared easily within teams.