Features

Active contributors: Rich Harris, Simon H, Dominic Gannaway

This section covers user-facing capabilities that span multiple parts of the codebase. Each page links into both the compiler-side and runtime-side implementation files.

Feature	What it covers
Runes	$state, $derived, $effect, $props, $bindable, $inspect, $host.
Transitions and animations	transition:, in:, out:, animate:, crossfade, flip.
Motion (springs and tweens)	The Spring and Tween reactive utilities (and legacy spring, tweened).
Stores	Legacy writable / readable / derived plus the new createSubscriber and toStore/fromStore interop.
Attachments and actions	{@attach}, createAttachmentKey, and the legacy use: action API.
Reactive built-ins	SvelteMap, SvelteSet, SvelteDate, SvelteURL, SvelteURLSearchParams, MediaQuery.
Boundary and async	<svelte:boundary>, {@async}, {#await}, async runes.
Custom elements	<svelte:options customElement> and the customElement runtime adapter.
Legacy compatibility	export let, $:, auto-subscribe stores, the migrate codemod.

For low-level subsystem details, see systems.