Blockly

Blockly is a client-side library for the programming language JavaScript for creating block-based visual programming languages (VPLs) and editors. A project of Google, it is free and open-source software released under the Apache License 2.0.^[2] It typically runs in a web browser, and visually resembles the language Scratch.

Blockly
Original authors	Neil Fraser, Quynh Neutron, Ellen Spertus, Mark Friedman
Developers	Google, MIT
Initial release	May 2012; 13 years ago (2012-05)
Stable release	12.1.0 / 30 May 2025; 5 months ago (2025-05-30)[1]
Repository	github.com/google/blockly
Written in	JavaScript
Platform	Web browser
Size	150 KB
Available in	50 languages
List of languages English
Type	Library
License	Apache License 2.0
Website	developers.google.com/blockly

• Computer programming portal
• Free and open-source software portal

Blockly uses visual blocks that help simplify programming, and can generate code in JavaScript, Lua, Dart, Python, or PHP. It can also be customized to generate code in textual programming language.^[3]

History

Blockly development began in summer 2011. The first public release was in May 2012 at Maker Faire. Blockly was originally designed as a replacement for OpenBlocks in App Inventor.^[4] Neil Fraser began the project with Quynh Neutron, Ellen Spertus, and Mark Friedman as contributors.

In October 2025, the Raspberry Pi Foundation announced that from 10 November 2025, the Blockly open source library and assets, and key members of the Blockly team will transition from Google to the Raspberry Pi Foundation.^[5]

User interface

Example of Blockly code to convert from Fahrenheit to Celsius

Example of Blockly code with a while loop

The default graphical user interface (GUI) of the Blockly editor consists of a toolbox, which holds available blocks, and where a user can select blocks, and a workspace, where a user can drag and drop and rearrange blocks. The workspace also includes, by default, zoom icons, and a trashcan to delete blocks.^[6] The editor can be modified easily to customize and limit the available editing features and blocks.

Customization

Blockly includes a set of visual blocks for common operations, and can be customized by adding more blocks. New blocks require a block definition and a generator. The definition describes the block's appearance (user interface) and the generator describes the block's translation to executable code. Definitions and generators can be written in JavaScript, or using a visual set of blocks, the Block Factory, which allows new blocks to be described using extant visual blocks; the intent is to make creating new blocks easier.

Applications

Blockly is used in several notable projects, including:

• MIT's Scratch (since version 3.0), visual programming environment for education^[7]
• MIT's App Inventor, to create applications for Android.^[8]
• MIT's CoCo, visual collaborative programming website for education.
• Code.org, to teach introductory programing to millions of students in their Hour of Code program^[9]
• Microsoft's MakeCode, "a free online learn-to-code platform where anyone can build games, code devices, and mod Minecraft" ^[10][11]
• RoboBlockly, a web-based robot simulation environment for learning coding and math
• PICAXE, to control their educational microchips^[12]

Features

• Web-based using Scalable Vector Graphics (SVG)
• Completely client-side JavaScript
• Support of major web browsers including: Chrome, Firefox, Safari, Opera, Edge
• Support for many programmatic constructs including variables, functions, arrays
• Minimal type checking supported, designed for dynamically typed languages
• Step-by-step code execution for tracing and debugging code^[13]
• Localised into 100+ languages^[14]
• Support for left-to-right and right-to-left languages^[15]