Svelte5 Best Practices

Published by denismrvoljak in pi-autoskills

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What this skill does

Svelte 5 runes, snippets, SvelteKit patterns, and modern best practices for TypeScript and component development. Use when writing, reviewing, or refactoring Svelte 5 components and SvelteKit applications. Triggers on: Svelte components, runes ($state, $derived, $effect, $props, $bindable, $inspect), snippets ({#snippet}, {@render}), event handling, SvelteKit data loading, form actions, Svelte 4 to Svelte 5 migration, store to rune migration, slots to snippets migration, TypeScript props typing,

Add Svelte5 Best Practices to your agent

Review the source and files first. When you are ready, copy the prompt instruction or use the CLI command supported by your environment.

Install with a prompt

Paste this into a compatible coding agent:

add this skill "svelte5-best-practices" from https://github.com/denismrvoljak/pi-autoskills

Install with the CLI

Run this command in a controlled environment after reviewing the repository:

npx skills add https://github.com/denismrvoljak/pi-autoskills --skill svelte5-best-practices

Skill instructions

Svelte 5 Best Practices

Quick Reference

Topic	When to Use	Reference
Runes	$state, $derived, $effect, $props, $bindable, $inspect	runes.md
Snippets	Replacing slots, {#snippet}, {@render}	snippets.md
Events	onclick handlers, callback props, context API	events.md
TypeScript	Props typing, generic components	typescript.md
Migration	Svelte 4 to 5, stores to runes	migration.md
SvelteKit	Load functions, form actions, SSR, page typing	sveltekit.md
Performance	Universal reactivity, avoiding over-reactivity, streaming	performance.md

Essential Patterns

Reactive State

<script>
  let count = $state(0);           // Reactive state
  let doubled = $derived(count * 2); // Computed value
</script>

Component Props

<script>
  let { name, count = 0 } = $props();
  let { value = $bindable() } = $props(); // Two-way binding
</script>

Snippets (replacing slots)

<script>
  let { children, header } = $props();
</script>

{@render header?.()}
{@render children()}

Event Handlers

<!-- Svelte 5: use onclick, not on:click -->
<button onclick={() => count++}>Click</button>

Callback Props (replacing createEventDispatcher)

<script>
  let { onclick } = $props();
</script>

<button onclick={() => onclick?.({ data })}>Click</button>

Common Mistakes

Using let without $state - Variables are not reactive without $state()
Using $effect for derived values - Use $derived instead
Using on:click syntax - Use onclick in Svelte 5
Using createEventDispatcher - Use callback props instead
Using <slot> - Use snippets with {@render}
Forgetting $bindable() - Required for bind: to work
Setting module-level state in SSR - Causes cross-request leaks
Sequential awaits in load functions - Use Promise.all for parallel requests

Files included

SKILL.md

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