All modules
MODULE 05 · HOW FRONTEND TALKS TO BACKEND
API layer
The card that makes tier moves cheap.
One typed client, one response shape — { data } on success, { error } on failure — from day one. Follow this card at Tier 1 and moving to a separate backend later is days, not months: the frontend just points at a new URL.
WHEN YOU NEED IT
Tier 1 and up. It matters most before you think you need it.
THE CHOICE, PER TIER
- T1Next.js Route Handlers, enveloped responses
- T2Separate Express service, same envelopes
- T3+ versioning, rate limits, request logging
SAY THIS TO YOUR AGENT
"Create a typed API client in one file. Every endpoint returns { data } or { error } with the same shape. All fetches go through the client — no raw fetch calls inside components."
DONE WHEN
- One file lists every endpoint the app calls
- Errors show a helpful message, never a blank screen
- Validation happens on the server, not just in forms