Subprojecttoctrees is a Sphinx extension that aims to facilitate the integration of several documentation sources into a single Read the Docs webpage. This project extends the Read the Docs subproject concept, which allows projects to be configured as as as subproject of another project, by creating a unified sidebar of URLs between these projects. A single ‘master’ index is specified in the ‘main’ project, eliminating the need to update all subprojects to change the index and allowing for version-specific sidebar links.