GitHub Pages can’t run custom Jekyll plug-ins so when generating Tables of Contents (TOCs), you’re stuck with either a JavaScript solution or using kramdown’s {:toc} option. However, by using {:toc}, you are forced to have that code next to your actual markdown and you can’t place it in a layout. This means every. single. post. will need to have the snippet. If you choose the JavaScript approach, that’s perfectly fine but what if JS is disabled on the someone’s browser or your page is just really long and it becomes inefficient. - Jekyll Pure Liquid Table of Contents

• Automatic Table of Contents
• Markdown All in One, TOC generation on edit

• Simple Table of Contents (ToC) Using Pure HTML and CSS Code

• Side Navigation (JS)