I know a lot of people use just and available free software for design however if you utilize Adobe Creative Suite as I do or Adobe Dreamweaver then you already have the tools in that development environment. Especially if you are using the new Dreamweaver CC which I believe is a $20-30 dollar a month software but that is cheap for what it gives you. You have a view for Phones, Tablets, Desktop so that you see how you site you build will look on all different devices and enable you to make changes on the fly.
However, unless you are using a design suite of this magnitude e.g. PROFESSIONAL level software you are gonna be hard pressed. If this is something you intend on doing for a living or intend on pursuing a career in well then Software is one of the biggest factors and best friends your gonna have especially on larger scale projects.