XBlock is a component architecture for building courseware. They are similar in structure to web applications.


The XBlock design recognizes a few different roles people can play:

Block Developer

An XBlock Developer is the author of an XBlock type. This is a Python developer writing Python classes to implement a new kind of XBlock.

Content Author

Original course material is written by a Content Author. This material may be made available to others to use in their own courses.

Course Assembler

A Course Assembler creates or modifies courses by using content created by someone else. Note that the same person can act as a content author and as a course assembler, often within the same authoring session.


The Student (or User) is whoever uses the web applications composed of XBlocks.


XBlocks are components that combine together to create interactive course content. They need to satisfy two conflicting goals: work together with other blocks to build a complete course; and be independent of other blocks, so they can be combined flexibly.

XBlocks are built similarly to web applications. They maintain state in a storage layer, render themselves through views, and process user actions through handlers.

They differ from web applications, though, because each XBlock renders only a small piece of a complete web page.


XBlocks do not run by themselves, they run within web applications such as Studio, or LMS, known as runtimes. Each runtime provides services to the XBlock, such as storage, URL mapping, and analytics.

Runtimes will differ in the context they provide to XBlocks. For example, while editing content, Studio won’t provide user state, because there is no interesting user state. Another runtime might provide user state, but as read-only data.

Runtimes also differ in what views they make use of. Studio might use “edit” to edit the XBlock content, and “read” to preview that content, while the LMS might only use the “read” view to render the XBlock for students. Each runtime is free to define view names it will use for its purposes. XBlock Developers need to understand the runtimes they will be running in to write the proper views.

Runtimes are responsible for performing any authentication needed before executing a view or handler in an XBlock.

Examples of runtimes:

  • Studio
  • LMS
  • XBlock debugging dashboard
  • Peer grading workflow app