CodePen vs. CodeTogether vs. JSFiddle vs. JavaScript Comparison Chart

CodePen is a social development environment for front-end designers and developers. Build and deploy a website, show off your work, build test cases to learn and debug, and find inspiration. Find inspiration from 1.8 million+ front-end designers and developers. Browse and share work from world-class designers and developers in the front-end community. The CodePen Editor is highly customizable. There is autocomplete and Emmet for speed and accuracy. Plus you can set up smart defaults for starting new work. Completely customize the look of code demos on your own site. Change the look of your site? Just change the theme and all your Embedded Pens change too. Need to use an image in a Pen? No more awkwardly finding alternate hosting for it, you can drag-and-drop it right onto CodePen and we'll host it for you. And not just images! CSS, JSON files, SVGs, media files, whatever! Projects is the most powerful feature of CodePen.

JSFiddle has the notion of panels (or tabs if you switch into the tabbed layout), there are 4 panels, 3 where you can enter code, and 1 to see the result: HTML - structure code, no need to add body doctype head, that's added automatically, CSS - styles. You can switch pre-pocessor to SCSS, JavaScript - behavior. There are many frameworks and code pre-processors you can use. Once you enter code, just hit "Run" in the top actions bar, and the fourth panel with results will appear. SFiddle allows you to switch the layout of the editor from the classic 2x2 grid to something that suits your needs. In addition to the grids mode it also has a tabbed mode. Grids are fully resizable. As an addition resizing the Results panel will tell you its width (handy for working on media queries).