ReddRadar
Agent skill
svelte5-development
Build web applications with Svelte 5 runes, SvelteKit routing, form actions, and component patterns. Use when working with Svelte, SvelteKit, or building reactive web interfaces.
Install this agent skill to your Project
npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/data/svelte5-development-autumnsgrove-groveengine
SKILL.md
Svelte 5 Development Skill
When to Activate
Activate this skill when:
- Creating Svelte 5 components
- Working with SvelteKit routing
- Implementing runes ($state, $derived, $effect)
- Building forms with actions
- Setting up SvelteKit projects
Quick Commands
npx sv create my-app # Create SvelteKit project
cd my-app && pnpm install
pnpm dev # Start dev server (localhost:5173)
pnpm build # Build for production
Runes Quick Reference
| Rune | Purpose | Example |
|---|---|---|
$state |
Reactive state | let count = $state(0) |
$derived |
Computed values | let doubled = $derived(count * 2) |
$effect |
Side effects | $effect(() => console.log(count)) |
$props |
Component props | let { name } = $props() |
$bindable |
Two-way binding | let { value = $bindable() } = $props() |
Reactive State ($state)
<script>
let count = $state(0);
let user = $state({ name: 'Alice', age: 30 });
let items = $state(['apple', 'banana']);
</script>
<button onclick={() => count++}>
Clicked {count} times
</button>
<button onclick={() => user.age++}>
{user.name} is {user.age}
</button>
Deep reactivity: Objects and arrays update automatically on mutation.
Computed Values ($derived)
<script>
let count = $state(0);
let doubled = $derived(count * 2);
// For complex computations
let summary = $derived.by(() => {
const total = items.length;
const done = items.filter(i => i.done).length;
return `${done}/${total}`;
});
</script>
Side Effects ($effect)
<script>
let count = $state(0);
$effect(() => {
console.log(`Count is ${count}`);
document.title = `Count: ${count}`;
// Cleanup function
return () => {
console.log('Cleanup');
};
});
</script>
Component Props ($props)
<!-- Button.svelte -->
<script>
let { label, disabled = false, onclick } = $props();
</script>
<button {disabled} {onclick}>{label}</button>
TypeScript Props
<script lang="ts">
interface Props {
label: string;
disabled?: boolean;
onclick?: () => void;
}
let { label, disabled = false, onclick }: Props = $props();
</script>
SvelteKit File Conventions
| File | Purpose |
|---|---|
+page.svelte |
Page component |
+page.server.js |
Server-only load/actions |
+layout.svelte |
Shared layout |
+server.js |
API endpoints |
+error.svelte |
Error boundary |
Data Loading
// src/routes/posts/+page.server.js
export async function load({ fetch }) {
const response = await fetch('/api/posts');
return { posts: await response.json() };
}
<!-- src/routes/posts/+page.svelte -->
<script>
let { data } = $props();
</script>
{#each data.posts as post}
<article>
<h2>{post.title}</h2>
</article>
{/each}
Form Actions
// src/routes/login/+page.server.js
import { fail, redirect } from '@sveltejs/kit';
export const actions = {
default: async ({ request, cookies }) => {
const data = await request.formData();
const email = data.get('email');
if (!email) {
return fail(400, { missing: true });
}
cookies.set('session', token, { path: '/' });
throw redirect(303, '/dashboard');
}
};
<!-- +page.svelte -->
<script>
import { enhance } from '$app/forms';
let { form } = $props();
</script>
<form method="POST" use:enhance>
<input name="email" value={form?.email ?? ''} />
{#if form?.missing}
<p class="error">Email required</p>
{/if}
<button>Submit</button>
</form>
API Routes
// src/routes/api/posts/+server.js
import { json } from '@sveltejs/kit';
export async function GET({ url }) {
const posts = await getPosts();
return json(posts);
}
export async function POST({ request }) {
const data = await request.json();
const post = await createPost(data);
return json(post, { status: 201 });
}
Common Pitfalls
Destructuring Breaks Reactivity
// ❌ Bad
let { count } = $state({ count: 0 });
// ✅ Good
let state = $state({ count: 0 });
state.count++;
Missing Keys in Each
<!-- ❌ Bad -->
{#each items as item}
<!-- ✅ Good -->
{#each items as item (item.id)}
Use Progressive Enhancement
<script>
import { enhance } from '$app/forms';
</script>
<form method="POST" use:enhance>
Project Structure
src/
├── lib/
│ ├── components/
│ └── server/
├── routes/
│ ├── +layout.svelte
│ ├── +page.svelte
│ └── api/
├── app.html
└── hooks.server.js
Related Resources
See AgentUsage/svelte5_guide.md for complete documentation including:
- Advanced rune patterns
- Snippets for reusable markup
- Performance optimization
- TypeScript integration
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