Once you have the single HTML file, you don't need an internet connection to play single-player worlds.

Simply right-click the downloaded file and select "Open with..." followed by your preferred browser.

Look for GitHub repositories or community Discord mirrors that provide the "Offline HTML" version.

Many school and office networks block the URLs of gaming sites. An offline file lives on your USB drive or local storage, making it nearly impossible to block.

Despite being a browser port, the Eaglercraft 1.5.2 exclusive build offers a surprisingly complete experience: