This is a web version of Lean 4. There is a playground hosted at live.lean-lang.org and one at lean.math.hhu.de.

In contrast to the Lean 3 web editor, in this web editor, the Lean server is running on a web server, and not in the browser.

• Provide a clean, minimalistic and easily accessible way to run some (smallish) Lean snippets
• Provide a simple way to run MWEs from Zulip with the latest Mathlib installed.
• Provide a easy way to demonstrate some Lean code in talks/lecutres.
• Provide a easy way for newcomers to doodle with Lean before installing it.
• Provide a way to run some Lean code in a mobile context.

Currently, serious Lean code development and larger projects are considered out-of-scope. For these, it might be more suitable to look at a setup using Codespaces or Gitpot.

While lean4web looks very similar to VSCode with the Lean4 extension installed - and it reuses much of that code - lean4web does not claim to be feature complete.

If you experience any problems, or have feature requests, please open an issue here!

PRs fixing issues are very welcome!

For new features, it's best to write an issue first to discuss them: For example, some functionality might be better implemented in lean4monaco which provides the key features and a discussion might be helpful to figure this out.

• User Manual: Specification of lean4web features for the end user.
• Installation: Instructions to install your own instance of lean4web on your own server
• Development: Instructions to contribute to lean4web itself