I use jekyll to build and test locally:
docker run --rm --volume=$(pwd):/srv/jekyll -v 'JEKYLL_ENV=production' -it -p 4000:4000 jekyll/jekyll jekyll serve
Every few months generate more webp versions of images: https://www.aleksandrhovhannisyan.com/blog/dev/improve-page-load-speed-in-jekyll-using-the-webp-image-format/