Plugin that allows you to insert a table of contents into your posts.
https://wordpress.org/plugins/easy-table-of-contents/
Widgets · WordPress Plugins
Get access to data on 69,604 websites that are Easy Table of Contents Customers. We know of 60,634 live websites using Easy Table of Contents and an additional 8,970 sites that used Easy Table of Contents historically and 36,607 websites in the United States.
Get a list of 69,604 websites using Easy Table of Contents which includes location information, hosting data, contact details, 60,634 currently live websites and an additional 14,167 domains that redirect to sites in this list. 8,970 sites that used this technology previously and 36,607 websites in the United States currently using Easy Table of Contents.