Svelte is a compiler-based UI framework that shifts work from runtime to build time, producing minimal JavaScript with no virtual DOM. Svelte 5 introduces runes for explicit, fine-grained reactivity. SvelteKit is the full-stack framework built on Svelte, providing file-based routing, server-side rendering, and deployment adapters.
When to use: Full-stack web apps, static sites, progressive enhancement, SSR/SSG, projects needing small bundle sizes, migration from Svelte 4 to 5.
When NOT to use: React/Vue ecosystem lock-in, projects requiring extensive third-party component libraries only available for other frameworks, teams with no Svelte experience on tight deadlines.
Svelte 5 and SvelteKit framework patterns. Covers runes ($state, $derived, $effect, $props, $bindable, $inspect), snippets, fine-grained reactivity, component composition, and event handling. SvelteKit coverage includes file-based routing, server and universal load functions, form actions, hooks, adapters, and error handling. Includes Svelte 4 to 5 migration guidance (stores to runes, on:event to onevent, slots to snippets). Use when building Svelte 5 components, configuring SvelteKit routing, implementing form actions, migrating from Svelte 4, or debugging reactivity issues. Source: oakoss/agent-skills.