How do you implement error handling in SvelteKit?

SvelteKit has a structured error handling system. Expected errors: throw with the error() helper in load functions or actions: import { error } from '@sveltejs/kit'; throw error(404, 'Post not found');. SvelteKit renders the nearest +error.svelte page. Create error pages at different route levels. Unexpected errors: unhandled exceptions in load functions. The handleError hook in hooks.server.js catches them: export function handleError({ error, event }) { Sentry.captureException(error); return { message: 'Something went wrong' }; }. The returned object becomes the error page's $page.error. +error.svelte: import { page } from '$app/stores'; <h1>{$page.error.message}</h1>. Client-side errors: hooks.client.js handleError for client-side navigation errors. This system ensures users always see a meaningful error page rather than a blank screen or cryptic message.