I've been working on something similar this year (https://www.entomic.com) that helps developers build cross-browser, responsive sites.
As an editor, all changes update immediately on all connected browsers and devices as they're being made to help see when things start going wrong.
Although it doesn't support javascript yet, all HTML and CSS changes do get pushed instantly to connected devices without the need to host a local server.
If you don't mind me asking, why did you choose to use a subscription model instead of a license that allows customers to own the app and just pay for updates if they need them? The subscription fee makes me hesitant to even try it. I like owning my tools, not renting them.
As an editor, all changes update immediately on all connected browsers and devices as they're being made to help see when things start going wrong.
Although it doesn't support javascript yet, all HTML and CSS changes do get pushed instantly to connected devices without the need to host a local server.