When comparing Notepad++ vs FlashDevelop, the Slant community recommends Notepad++ for most people. In the question“What are the best programming text editors?” Notepad++ is ranked 15th while FlashDevelop is ranked 41st. The most important reason people chose Notepad++ is:
Notepad++ has built-in support for syntax highlighting for a wide selection of programming languages.
Specs
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Pros
Pro Syntax highlighting for a wide variety of languages
Notepad++ has built-in support for syntax highlighting for a wide selection of programming languages.
Pro Light and fast
Notepad++ is a very light program that starts almost instantly. This makes it a great text editor for users that want something that will start the second they open it.
Pro Extendable via plugins
A list of hundreds of plugins is maintained.
Pro Portable
You can get a portable version of N++ and put it on a flash drive or your dropbox account and have your editor, configured the way you like, at any computer that you are on.
Pro Free under GPL
Notepad++ is licensed under GPL, which means it is free/open source software that you can use freely.
Pro Regex replace in selection, active tab, or all tabs
In Notepad++, the user can utilise regular expressions to quickly modify text across multiple files.
Pro Persistent documents, even after exiting the application
If you close Notepad++ (npp), your documents remain even if you haven't saved.
Pro User defined language syntax support
You can define your own custom syntax highlighting rules (or add support for others) .
Pro Easy to use and admin
Very easy to use and personalize.

Pro Multi-line editing
While it is disabled by default, when enabled, it is possible to edit more than one line at a time. This is helpful in many situations.
Pro Split screen
The user can open and edit files in multiple screens within the editor window.
Pro Supports Markdown
If you have the Plugin Manager installed you can search for MarkdownViewer++ and install it via that plugin.
Pro Free
FlashDevelop comes without any cost.
Pro Haxe development support
FlashDevelop has first-class support for Haxe development, the open source toolkit based on a modern programming language and cross-platform library.
Pro Good code completion
FlashDevelop's code completion is pretty good.
Pro Excellent support for Actionscript 2 and 3 (Flash)
Although everyone claims Flash is dead, it's still quite useful for game developers due to its rapid compile and run times, as well as its great debugging functionality with FlashDevelop.
Pro Good number of project templates
While it's project template system is not the best compared to it's competitors, it still is decent and is a good way to generate some boilerplate code.
Pro XML/HTML completion
FlashDevelop has XML/HTML completion aside from code completion.
Pro .NET Framework 2.0 application
It's windows only, but has tremendous support from plugin developers and a dedicated team that's been developing it for close to 10 years.
Pro Source-control support (svn, git, mercurial)
Pro Great debugging
FlashDevelop provides very efficient debugging features.
Pro Supports Zen-coding for HTML
This is very useful for carrying out high-speed HTML coding and editing.
Pro Snippets
Pro Tasks/todo
Pro SWF/SWC exploration
Pro Great project compilation
FlashDevelop facilitates project compilation.
Pro Decent code generation
Although the code generation can't really be called top-notch, it's decent and sufficient for most developers.
Cons
Con Windows-only
While it can run in Wine, it is native only to Windows. Linux users will have to use Notepadqq instead.
Con Settings confusingly scattered
Examples: try to change the tab size or used font.
Con Annoying update notifications upon start-up
Annoying update notifications tend to pop up upon start-up after not having used the app or machine for a few days. At the same time, they can be easily turned off.
Con Outdated UI
Only the text area can be themed, and it doesn't have as many features as browser-based text areas.
Con Limited new syntax support for new languages
It may be hard to find good plugins for relatively new languages.
Con Session backups not enabled by default
Unsaved tabs will be lost when Npp crashes, unless you first enable the session backup option.
Con User defined language doesn't support triple quote strings
It also doesn't support triple hashed comments. Both styles are overridden by their single character single line version.
Con Windows only
FlashDevelop is for Windows only, and it's not cross-platform either.
Con Haxe debugging is in its infancy
Although FlashDevelop supports breakpoint debugging on Flashplayers, native Haxe applications (C++) can't be easily debugged within FlashDevelop.
