Build the API First — Why It Saves Money Later

A lot of systems start as a web app. Then a mobile app is added, and because there was no shared API, the mobile developer rebuilds the same business rules again — slightly differently. Now a discount works one way on the website and another way in the app.

One place for the rules

An API-first design puts the logic — pricing, stock, permissions, validation — behind one interface that every client calls. Change the discount rule once and the website, the app and the dealer portal all follow. That's the whole benefit, and it's a big one.

Things worth deciding early

• Authentication — tokens, expiry and refresh, agreed once
• Consistent error shapes so clients handle failures the same way
• Pagination on every list that can grow
• Versioning, so an app update doesn't break old installs
• Rate limiting before someone finds the endpoint, not after

The version problem is real

You control your website. You don't control who updates their phone. Old app versions will keep calling your API for months, so plan to support them — add fields rather than renaming them, and never remove one without a deprecation period.