Svelte Core Best Practices

What it does

When your agent uses it

• Writing or editing a Svelte component or module
• Deciding whether to use state, derived or an effect
• Syncing Svelte state to an external library such as D3

Example prompts

• “Refactor this component to use $derived instead of an effect for the computed total.”
• “Add a Svelte binding so the child component can update the parent's selected tab.”
• “Why does my $effect run on the server? Fix it the idiomatic way.”

Requirements

• A Svelte 5 project

What it can do on your machine

Read from SKILL.md and the folder at commit 8447fa4. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md (its code samples are svelte and javascript).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Svelte Core Best Practices loads about 1.8k tokens when it runs, and up to ~8.6k if it reads all its reference files. Until then it costs about 68 tokens; SKILL.md has 841 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~68

When it runs · the whole SKILL.md, loaded when a task matches

~1.8k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~8.6k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from rilldata/rill at commit 8447fa4, republished under its Apache-2.0 licence (© rilldata). 841 words, ~1,802 tokens.

name

svelte-core-bestpractices

description

Guidance on writing fast, robust, modern Svelte code. Load this skill whenever in a Svelte project and asked to write/edit or analyze a Svelte component or module. Covers reactivity, event handling, styling, integration with libraries and more.

glob

**/*.svelte{,.*}

// do this
let square = $derived(num * num);

// don't do this
let square;

$effect(() => {
	square = num * num;
});

// @errors: 2451
let { type } = $props();

// do this
let color = $derived(type === 'danger' ? 'red' : 'green');

// don't do this — `color` will not update if `type` changes
let color = type === 'danger' ? 'red' : 'green';

<button onclick={() => {...}}>click me</button>

<!-- attribute shorthand also works -->
<button {onclick}>...</button>

<!-- so do spread attributes -->
<button {...props}>...</button>

<svelte:window onkeydown={...} />
<svelte:document onvisibilitychange={...} />

{#snippet greeting(name)}
	<p>hello {name}!</p>
{/snippet}

{@render greeting('world')}

<div style:--columns={columns}>...</div>

<!-- Parent.svelte -->
<Child --color="red" />

<!-- Child.svelte -->
<h1>Hello</h1>

<style>
	h1 {
		color: var(--color);
	}
</style>

<div>
	<Child />
</div>

<style>
	div :global {
		h1 {
			color: red;
		}
	}
</style>

© rilldata, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 9 other files (references) in .claude/skills/svelte-core-bestpractices of rilldata/rill.

• SKILL.md
• references/$inspect.md
• references/@attach.md
• references/@render.md
• references/await-expressions.md
• references/bind.md
• references/each.md
• references/hydratable.md
• references/snippet.md
• references/svelte-reactivity.md

Open the folder on GitHubat commit 8447fa4

Used in 4 other repositories

We found 4 copies of this SKILL.md (exact, near-identical or edited) in other folders, from 4 other GitHub owners. This page covers the copy in rilldata/rill, which our catalogue first saw on October 7, 2026.

• kampsy/ui.agents/skills/svelte-core-bestpractices
• Open-TutorAi/open-tutor-ai-CE.agents/skills/svelte-core-bestpractices
• regisx001/Worklog.github/skills/svelte-core-bestpractices
• getopenpost/openpostapps/web/.agents/skills/svelte-core-bestpractices