Startup Idea: Automated Browser and Device Emulation Software for Web Design Testing

Startup idea to develop a software that enables freelance web designers to automate the process of testing their designs on different browsers and devices. The software should also be capable of taking full page screenshots of specific resolutions on a local host.

I'm a freelance web designer (very little back-end development experience) working with content management systems developed in a local environment.

A big pain point for me is testing designs by emulating different devices and browsers. There are a few services that do this through web servers, and it can be done manually, but it's hard to find actual software that will automate the process and take full page screenshots for me.

If there was a program that would allow me to enter a full range of browsers and devices and take screenshots at specific resolutions (full page) on a local host and name/organize the screenshots appropriately I would definitely purchase as a one time fee, or with a subscription model at a fair rate (around $10 USD per month?). Live testing with touch emulation would be a plus.

Such a program would save me a ton of time when I'm going through mock-ups and presenting designs.