The article

Every design breaks at handoff in the same five places: missing states, mystery spacing, unexplained motion, fake data that hides edge cases, and “just make it responsive”. Our checklist exists so none of those survive to the sprint.

First, tokens before screens. Spacing, type, colour and radius ship as named tokens both sides consume. If a value appears twice in the UI and once in the code under a different name, the system is already lying.

Design every state a component can be in — loading, empty, error, offline, overflowing — or developers will invent them for you.

Second, annotate behaviour, not appearance. Engineers can see the padding; they cannot see that the card dismisses on swipe only after a 200ms delay, or that the chart animates on data change but not on filter change. We pin behaviour notes directly on the frame, dated, so stale notes die visibly.

Third, design with ugly data. Long German button labels, 400-character names, zero search results, a user with fourteen payment methods. Real data is a stress test the happy path never survives.

Finally, sit in the build. Our designers review staging weekly and file layout bugs in the same tracker as everyone else. Handoff is not a phase — it is a seat at the table until release.