This is a web version of Lean 4. The official lean playground is hosted at live.lean-lang.org, while lean.math.hhu.de hosts a development server testing newer features.

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.

If you experience any problems, or have feature requests, please open an issue here! PRs are welcome as well.

To add new themes, please read Adding Themes.

Providing the use access to a Lean instance running on the server is a severe security risk. That is why we start the Lean server using Bubblewrap.

We have set up the project on a Ubuntu Server 22.10. Here are the installation instructions:

Install NPM (don't use apt-get since it will give you an outdated version of npm):

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.2/install.sh | bash
source ~/.bashrc
nvm install node npm

Now, install git and clone this repository:

sudo apt-get install git
git clone https://github.com/leanprover-community/lean4web.git

Install Bubblewrap:

sudo apt-get install bubblewrap

Navigate into the cloned repository, install, and compile:

cd lean4web
npm install
npm run build

Now the server can be started using

PORT=8080 npm run production

To set the locations of SSL certificates, use the following environment variables:

SSL_CRT_FILE=/path/to/crt_file.cer SSL_KEY_FILE=/path/to/private_ssl_key.pem PORT=8080 npm run production

Optionally, you can set up a cronjob to regularly update the mathlib version. To do so, run

crontab -e

and add the following lines, where all paths must be adjusted appropriately:

# Need to set PATH manually:
SHELL=/usr/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/home/USER/.elan/bin:/home/USER/.nvm/versions/node/v20.8.0/bin/

# Update server (i.e. mathlib) of lean4web and delete mathlib cache
*  */6 * * * cd /home/USER/lean4web && npm run build_server 2>&1 1>/dev/null | logger -t lean4web
40 2   * * * rm -rf /home/USER/.cache/mathlib/

Note that with this setup, you will still have to manage the lean toolchains manually, as they will slowly fill up your space (~0.9GB per new toolchain): see elan toolchain --help for infos.

In addition, we use Nginx and pm2 to manage our server.

Running and updating the server periodically might accumulate lean toolchains.

To delete unused toolchains automatically, you can use the elan-cleanup tool and set up a cron-job with crontab -e and adding the following line, which runs once a month and deletes any unused toolchains:

30 2 1 * * /PATH/TO/elan-cleanup/build/bin/elan-cleanup | logger -t lean-cleanup

You can see installed lean toolchains with elan toolchain list and check the size of ~/.elan.

For legal purposes, we need to display contact details. When setting up your own server, you will need to modify the following files:

• client/src/config/text.tsx: Update contact information & server location. (set them to null if you don't need to display them in your country)
• client/public/index.html: Update the noscript page with the correct contact details.

Install npm and clone this repository. Inside the repository, run npm install to install dependencies, and then npm start. The project can be accessed via http://localhost:3000. (Internally, websocket requests to ws://localhost:3000/websockets will be forwarded to a Lean server running on port 8080.)