SQL Data Catalog allows users to catalog their SQL Server data estate by applying classifications, as tags and free-text labels, to SQL Server objects. The taxonomy of tags and attributes to be applied is also created and managed. A common use case for SQL Data Catalog is for classifying columns by their sensitivity under data privacy regulations such as the GDPR. SQL Data Catalog is a web application backed by a Windows Service and a SQL Server database. The application has a web UI, and also exposes an API that can be used to query the Data Catalog directly.