When Go is the right boundary
A Go backend is useful when the product benefits from explicit service boundaries, predictable deployment artifacts, server-owned business rules, and a language well suited to concurrent application work. It also creates an operational cost: the frontend and API become separate runtimes.
Choose a Go + Next.js starter because the product needs that split today, not because a second runtime sounds more enterprise. A single Next.js application is the more honest choice for many early products.
Tenancy before feature count
Multi-tenancy affects identity, authorization, database access, background jobs, cache keys, files, webhooks, and administration. A tenant_id column on a few tables is not a complete isolation model.
A useful Go SaaS foundation makes tenant context explicit at trusted server boundaries and keeps cross-tenant negative tests permanent as the domain grows.
Authorization stays server-side
RBAC should describe which action an identity may perform inside a tenant, while tenant membership describes where that identity may operate. The API must enforce both; hiding a navigation item in Next.js is only interface behavior.
The implementation should make delegated authorization, tenant context, and PostgreSQL row-level security assumptions testable rather than burying them in interface conventions.
Billing is a lifecycle
A checkout page is the beginning of billing, not the end. Review webhook signature verification, idempotency, subscription transitions, invoices, reconciliation, fulfillment, and how every operation stays tenant-aware.
Provider secrets and fulfillment decisions belong on the server. The browser should never become the authority for payment state.
Know what source ownership includes
A source-code license should state the repositories or artifacts delivered, permitted commercial use, repository-user limits, update period, support boundary, and exclusions. It should also be clear whether hosting or custom implementation is included.
Amsonia Platform is a commercial source package. The buyer controls customization and deployment; Willuny Labs remains the seller and support boundary for the selected package.