Useful Tools All Web Developers Should Check Out

I've been into web development for some years now, and I must say, it's a great experience. Over the years I've come across some tools that makes my work easier and more enjoyable. This discussion is purposed to share some of these tools with you.
Here they are:

1. Emmet
Emmet is a plugin for many popular text editors which greatly improves the speed with which you write HTML by allowing you to transform CSS-like selectors into full-blown HTML very fast.
I use Emmet with Sublime Text, and I tell you, my life never remained the same since I started using it.

2. SublimeText
Sublime Text is a simple/sophisticated text editor that lets you type in and play around code in amazing ways.

3 Domai.nr
Domai.nr lets you check the availability of a domain name and get suggestions on similar names. Works quite well, and fast too. Another tool I use for domain search is Lean Domain Search, which checks thousands of domains for availability for you.

4. Whats my browser size?
I use this tool a lot when working on responsive pages (writing css media queries). It measures the size of your browser window. Simple as that but very useful nonetheless.

5. JSONView
When working with APIs this tool comes in very handy for me. A Chrome and Firefox add-on for reading and validating JSONs in the browser.

Have you used any of this tools? What are your best web development tools?