Day 009 - Tools - Online
When working on bigger projects that may contain hundreds or thousands of lines of code and you're working on something that's not quite working the way you want it, a great approach is to create a 'reduced test case'.
Some awesome people have created the following sites that make it great to quickly create a reduced test case and even better, allow you to save, edit and share your code.
They're also great for trying out new techniques and playing about with code that's new or you're not familiar with.
Enjoy!