Not hard laws, but practical signals that usually mark the turning point.
More than one user role
Once clients, employees or partners need different permissions, a web app is often the better fit.
More than one external integration
As soon as data must move between multiple systems, a standard website quickly runs out of room.
Persistent process statuses
Think of intake, planning, service or document flows that users need to revisit later.
Custom calculations or exception logic
If pricing, routing or approval depends on your own rules, custom software usually becomes relevant.
Repeatable follow-up should run automatically
If tasks, alerts or next steps should no longer be tracked manually, a web app is often the better base.