"Design multi-tenant applications with deliberate data isolation, trusted tenant context, tenant-aware authorization, and boundary testing."

Building software for one organization is different from building software that serves many organizations.

This distinction has become particularly relevant to me through work around school-management software.

When an application serves a single organization, many assumptions can remain implicit. Users belong to the same organizational environment. Configuration is relatively straightforward. Data access often assumes a single administrative boundary.

Those assumptions become dangerous when the same application serves multiple organizations.

A school-management platform, for example, may serve hundreds of schools, each with its own students, teachers, classes, academic sessions, billing arrangements, and administrative policies.

The application may share infrastructure, but the organizations using it must remain distinct in the ways that matter to the…