Microsoft Graph Schema Extensions

Microsoft Graph schema extensions let you add your own strongly typed fields to Microsoft 365 resourcessuch as users, groups, messages, events, devices, and moreso your applications data can live alongside Microsoft data and be accessed through the same Graph APIs. You register a schema extension (with a unique ID tied to your verified domain), define property names and types, and then write values to individual resource instances; those values are returned with the resource and can be selected or, on supported entities, filtered in queries. Unlike untyped open extensions, schema extensions are discoverable and enforce types, making them easier to share across apps and tenants and to manage through a defined lifecycle. This approach reduces the need for a separate store or custom service, keeps data consistent and secured under Microsoft Graphs auth model, and enables richer, domain-specific solutions built on top of Microsoft 365.