SvelteKit Data Flow

Quick Start

Environment variables: Prefer explicit env vars (src/env.ts + $app/env/private|public) when the experimental flag is enabled.

Which file? Server-only (DB/secrets): +page.server.ts | Universal (runs both): +page.ts | API: +server.ts

Load decision: Need server resources? → server load | Need client APIs? → universal load

Form actions: Always +page.server.ts. Return fail() for errors, throw redirect() to navigate, throw error() for failures.

Example