When comparing StackEdit vs IntelliJ IDEA, the Slant community recommends StackEdit for most people. In the question“What are the best Markdown editors for OS X?” StackEdit is ranked 3rd while IntelliJ IDEA is ranked 23rd. The most important reason people chose StackEdit is:
StackEdit works within your browser. You need internet access to connect to the website, but once it's loaded, the site does not require an internet connection - you will be able to edit and save files locally. Additionally, you can use [Fluid](http://fluidapp.com) to turn it into a native desktop application.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Works online and offline
StackEdit works within your browser. You need internet access to connect to the website, but once it's loaded, the site does not require an internet connection - you will be able to edit and save files locally. Additionally, you can use Fluid to turn it into a native desktop application.
Pro Supports various Markdown flavors
Supports standard Markdown and Markdown Extra.

Pro Simple workflow
It is very easy to toggle between the preview and the editing windows. The black makes it a very focused writing environment. Of course it's possible to change that if needed.

Pro Great when in full-screen
Pro No need to install additional software
StackEdit works directly from the browser, there's no need to install additional software as long as you have a web browser installed on your computer.
Pro Real-time preview
The preview shows in a collapsible pane on the right hand side.
Pro Instant publishing
StackEdit allows pushing a document directly to a list of publishing or file storage platforms or any SSH server.
Pro Multiple export options
Can export to .txt, .html and .pdf.
Pro Syncs via Dropbox and Drive
Files can be synchronized through Dropbox and Drive.
Pro Great Java Support
Pro A good editor for test-driven development
IntelliJ IDEA is really easy to work with when it comes to test-driven development in Java and JavaScript/TypeScript.
Pro Great JavaScript support
Pro Markdown support with preview
Pro Supports PHP quite well
Pro Great TypeScript support
Really good support for importing classes, libraries, etc. into a typescript class. Making it easy to do TDD.
Pro Good BASH script support
Pro Angular CLI support
Pro Made by developers for developers
It can make one more efficient, but also can get one way too used to shortcuts, autocomplete, and easy debugging.
Cons
Con Saves files in browser's local storage
Local storage is limited and if the browser crashes the text can be lost.
Con Cannot be accessed while being offline
Even though the editor itself works offline, you need internet access to open the website and the editor.
Con Lacks a good integrated spell checker
Uses the built-in browser spell checker which may not be as good as spell checkers other editors have. Depending on the browser, of course.
Con Publishing to GitHub requires giving write access to repos
In order to publish documents to GitHub, StackEdit requires writing access to your repos, something which many people may not be comfortable with.
Con Is not free
But it does have a free version (Community Edition).
Con Heavy
Consumes more resources than VSCode etc. But depending on your use-case, it can still be worth it for the benefits you get with this editor.
Con Autocomplete does not work while IntelliJ is indexing
But this, in general, is not much of an issue. Usually after npm install, etc.
