Blockly is a client-side library for the programming language JavaScript for creating block-based visual programming languages (VPLs) and editors. It is a project of Google and is free and open-source software released under the Apache License 2.0. It typically runs in a web browser, and visually resembles the language Scratch. Blockly is also being implemented for the mobile operating systems Android and iOS, though not all web browser based features are available for these.
Blockly uses visual blocks that link together to make writing code easier, and can generate code in JavaScript, Lua, Dart, Python, or PHP. It can also be customised to generate code in any textual programming language.