> For the complete documentation index, see [llms.txt](https://docs.imerit.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.imerit.net/core-concepts/label-sets-ontologies.md).
# Category Schema (Ontologies)
A project’s category schema (also known as *ontology*) is the list of labeling tools available in the project.
Ango Hub allows project owners to set the project’s ontology directly from the *Category Schema* section of the *Settings* page.
The ontology created from this section is then reflected in the left sidebar of the labeling editor:
## How to create a project ontology
From the project’s *Settings* tab, enter the *Label Set* section.
Click on the *Add Category* button and choose the labeling tool to add. Each tool has a slightly different setup process. [See here for a list of all labeling tools available in Ango Hub, and how to add them to your project.](/labeling/labeling-tools.md)
For a guide on how to create nested classifications, [see here](/labeling/labeling-tools/tools/nested-classifications.md).
## How to copy a project's ontology to a new project
Please [check this guide](/how-to/transfer-project-ontologies-between-projects.md).
## Browse and Restore Previous Ontology Versions
From the Settings tab, in the *Category Schema* section, click on the "History" icon on the top-right to open a history of all workflow versions in the current project.
{% hint style="info" %}
Category Schema history started being recorded on March 12, 2025. Versions before then had not been saved.
{% endhint %}
To view a previous version of this project's ontology, click on *Preview*. To restore it, click on *Save* while the version you need is previewed.