Taming the Front-End Monolith (blog.logrocket.com)

it would be cool to have a standalone tool like Postman that works without internet

Interestingly my company is working on something that seeks to solve the same problem. It is called Podium and was recently open-sourced: https://podium-lib.io/

While it is still under active development we are using it in production for quite a lot of our new projects and it have worked very well for us so far!