Haxe is an open-source high-level cross-platform programming language and compiler that can produce applications and source code, for many different computing platforms from one code-base. It is free and open-source software, released under the MIT License. The compiler, written in OCaml, is released under the GNU General Public License (GPL) version 2.

Haxe includes a set of features and a standard library supported across all platforms, like numeric data types, strings, arrays, maps, binary, reflection, math, http, file system and common file formats. Haxe also includes platform-specific APIs for each compiler target. Kha, OpenFL and Heaps.io are popular Haxe frameworks that enable creating multi-platform content from one codebase.

Haxe originated with the idea of supporting client-side and server-side programming in one language and simplifying the communication logic between them. Code written in the Haxe language can be compiled into JavaScript, C++, Java, JVM, PHP, C#, Python, Lua and Node.js. Haxe can also directly compile SWF, HashLink and Neko, bytecode and also runs in interpreted mode.

Haxe supports externs (definition files) that can contain type information of existing libraries to describe target-specific interaction in a type-safe manner, like C++ header files can describe the structure of existing object files. This enables it to use the values defined in the files as if they were statically typed Haxe entities. Besides externs, other solutions exist to access each platform's native capabilities.

Many popular IDEs and source code editors have support available for Haxe development. No particular development environment or tool set is officially recommended by the Haxe Foundation, although VSCode, IntelliJ IDEA and HaxeDevelop have the most support for Haxe development. The core functionalities of syntax highlighting, code completion, refactoring, debugging, etc. are available in various degrees.