They do cost money unfortunately, but what you could do is use a tool like https://whimsical.com/wireframes to wireframe your website (free if you keep all files in your personal folder). Then use tailwindui or flowbite as a reference (or some other template library) while wireframing, skip the mockup stage, and then go straight into the coding phase? Source: 11 months ago

Just so you know Sizzy exists as well and has been around for a while so you would competing with them as well. Source: 6 months ago

I would like to introduce you to Sizzy. Source: about 1 year ago

Sizzy is the only exception I've found to date, but while being a nice for development it's not useful as an everyday browser. Source: over 1 year ago

I am personally debating on buying this eventually https://sizzy.co. Right now I use the built in Safari tool for testing on multiple iOS devices, but this will allow me to test on multiple device types. Source: over 1 year ago

There's also Sizzy (https://sizzy.co). It's available standalone, but it's also included with a Setapp subscription (https://setapp.com — Mac app subscription service). - Source: Hacker News / over 1 year ago