svelte-runes - SKILL.md Agent Skill

name: svelte-runes

IMPORTANT: Keep description on ONE line for Claude Code compatibility

prettier-ignore

description: Svelte runes guidance. Use for reactive state, props, effects, attachments, or migration. Covers $state, $derived, $effect, @attach. Prevents reactivity mistakes.

Svelte Runes

Quick Start

Which rune? Props: $props() | Bindable: $bindable() | Computed: $derived() | Side effect: $effect() | State: $state()

Key rules: Runes are top-level only. $derived can be overridden (use const for read-only). Don't mix Svelte 4/5 syntax. Objects/arrays are deeply reactive by default.

Example

<script>
    let count = $state(0); // Mutable state
    const doubled = $derived(count * 2); // Computed (const = read-only)

    $effect(() => {
        console.log(`Count is ${count}`); // Side effect
    });
</script>

<button onclick={() => count++}>
    {count} (doubled: {doubled})
</button>

Reference Files

reactivity-patterns.md - When to use each rune
migration-gotchas.md - Svelte 4→5 translation
component-api.md - $props, $bindable patterns
snippets-vs-slots.md - New snippet syntax
common-mistakes.md - Anti-patterns with fixes
attachments.md - @attach replaces use: actions

Notes

Use onclick not on:click, {@render children()} in layouts
$derived can be reassigned (5.25+) - use const for read-only
Last verified: 2025-01-11