| name | error-states |
| description | Design the non-happy-path UI in Next.js — loading, error, not-found, and empty states with Suspense, error boundaries, and user-facing feedback. Use when a page fetches data, can fail, or can be empty. |
error-states
Most apps ship the happy path and forget the other three. A surface isn't done until loading, empty, and
error are all handled.
The four states for every data surface
- Loading —
loading.tsx or <Suspense fallback>. Use skeletons that match the final layout (no CLS),
not a bare spinner where possible.
- Empty — designed empty state with a next action ("No projects yet — create one"), not a blank box.
- Error —
error.tsx (client error boundary) with a human message + a retry (reset()); log the real
error server-side. Never show a raw stack trace to users.
- Not found —
not-found.tsx + notFound() for missing resources (real 404, not a 200 with "nothing here").
Feedback for actions
- Mutations show pending state (disabled + spinner) and a success/error toast (
aria-live for errors).
- Optimistic updates roll back visibly on failure (see
state-architect).
Output
- The loading/empty/error/not-found treatments for the surface, and the action feedback.
- State which of the four are implemented and which are N/A.
Guardrails
- No surface ships with only the happy path.
- Error UI must not leak internal details; log them server-side instead.
- Skeletons must reserve the real layout's space to avoid layout shift.
