> ## Documentation Index
> Fetch the complete documentation index at: https://handbook.aiql.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Ontologies API

> Catalog and introspection of source shapes

The **Ontologies API** at [ontologies.aiql.io](https://ontologies.aiql.io) serves the schema catalog. It stores and returns the *shape* of connected sources: classes, data properties, and object properties. It does not store row-level data.

The catalog holds source types such as databases and APIs. Posting a source URL to a type introspects that source and builds a schema instance others can reuse.

This API is the programmatic surface of the [Ontologies](/products/ontologies) product. Studio's in-workspace ontology views apply a shape inside a workspace so Observatory can reason. The Ontologies API is the directory and introspection layer for those shapes.

Related APIs: [Middleware API](/products/middleware), [Connectors API](/products/connectors-api).