If your GitHub Pages code includes a reference to an invalid submodule, your GitHub Pages site will not build.

If your GitHub Pages site fails to build because of an invalid submodule, you'll get an email with this message:

Subject: Page build failed

The page build failed with the following error:

"The submodule registered for `./EXAMPLE_SUBMODULE` could not be cloned. Make sure it's using https:// and that it's a public repo.

Troubleshooting invalid submodule errors

Tip: We strongly recommend running Jekyll locally so you can easily debug and fix build errors before pushing to GitHub. To learn more about troubleshooting options, see "Troubleshooting GitHub Pages builds."

Check the submodule referenced in the build failure email. Ensure that:

  • You use https:// when referencing the submodule, not http://.
  • The submodule is in a public repository. The GitHub Pages server cannot build from submodules in private repositories.

Once you've fixed all invalid submodule errors, you will need to commit your changes and push to your GitHub Pages repository again to trigger another build on the server.