No,Category,Guideline,Description,Do,Don't,Code Good,Code Bad,Severity,Docs URL
1,Reactivity,Use $: for reactive statements,Automatic dependency tracking,$: for derived values,Manual recalculation,$: doubled = count * 2,let doubled; count && (doubled = count * 2),Medium,https://svelte.dev/docs/svelte-components#script-3-$-marks-a-statement-as-reactive
2,Reactivity,Trigger reactivity with assignment,Svelte tracks assignments not mutations,Reassign arrays/objects to trigger update,Mutate without reassignment,"items = [...items, newItem]",items.push(newItem),High,https://svelte.dev/docs/svelte-components#script-2-assignments-are-reactive
3,Reactivity,Use $state in Svelte 5,Runes for explicit reactivity,let count = $state(0),Implicit reactivity in Svelte 5,let count = $state(0),let count = 0 (Svelte 5),Medium,https://svelte.dev/blog/runes
4,Reactivity,Use $derived for computed values,$derived replaces $: in Svelte 5,let doubled = $derived(count * 2),$: in Svelte 5,let doubled = $derived(count * 2),$: doubled = count * 2 (Svelte 5),Medium,
5,Reactivity,Use $effect for side effects,$effect replaces $: side effects,Use $effect for subscriptions,$: for side effects in Svelte 5,$effect(() => console.log(count)),$: console.log(count) (Svelte 5),Medium,
6,Props,Export let for props,Declare props with export let,export let propName,Props without export,export let count = 0,let count = 0,High,https://svelte.dev/docs/svelte-components#script-1-export-creates-a-component-prop
7,Props,Use $props in Svelte 5,$props rune for prop access,let { name } = $props(),export let in Svelte 5,"let { name, age = 0 } = $props()",export let name; export let age = 0,Medium,
8,Props,Provide default values,Default props with assignment,export let count = 0,Required props without defaults,export let count = 0,export let count,Low,
9,Props,Use spread props,Pass through unknown props,{...$$restProps} on elements,Manual prop forwarding,<button {...$$restProps}>,<button class={$$props.class}>,Low,https://svelte.dev/docs/basic-markup#attributes-and-props
10,Bindings,Use bind: for two-way binding,Simplified input handling,bind:value for inputs,on:input with manual update,<input bind:value={name}>,<input value={name} on:input={e => name = e.target.value}>,Low,https://svelte.dev/docs/element-directives#bind-property
11,Bindings,Bind to DOM elements,Reference DOM nodes,bind:this for element reference,querySelector in onMount,<div bind:this={el}>,onMount(() => el = document.querySelector()),Medium,
12,Bindings,Use bind:group for radios/checkboxes,Simplified group handling,bind:group for radio/checkbox groups,Manual checked handling,"<input type=""radio"" bind:group={selected}>","<input type=""radio"" checked={selected === value}>",Low,
13,Events,Use on: for event handlers,Event directive syntax,on:click={handler},addEventListener in onMount,<button on:click={handleClick}>,onMount(() => btn.addEventListener()),Medium,https://svelte.dev/docs/element-directives#on-eventname
14,Events,Forward events with on:event,Pass events to parent,on:click without handler,createEventDispatcher for DOM events,<button on:click>,"dispatch('click', event)",Low,
15,Events,Use createEventDispatcher,Custom component events,dispatch for custom events,on:event for custom events,"dispatch('save', { data })",on:save without dispatch,Medium,https://svelte.dev/docs/svelte#createeventdispatcher
16,Lifecycle,Use onMount for initialization,Run code after component mounts,onMount for setup and data fetching,Code in script body for side effects,onMount(() => fetchData()),fetchData() in script body,High,https://svelte.dev/docs/svelte#onmount
17,Lifecycle,Return cleanup from onMount,Automatic cleanup on destroy,Return function from onMount,Separate onDestroy for paired cleanup,onMount(() => { sub(); return unsub }),onMount(sub); onDestroy(unsub),Medium,
18,Lifecycle,Use onDestroy sparingly,Only when onMount cleanup not possible,onDestroy for non-mount cleanup,onDestroy for mount-related cleanup,onDestroy for store unsubscribe,onDestroy(() => clearInterval(id)),Low,
19,Lifecycle,Avoid beforeUpdate/afterUpdate,Usually not needed,Reactive statements instead,beforeUpdate for derived state,$: if (x) doSomething(),beforeUpdate(() => doSomething()),Low,
20,Stores,Use writable for mutable state,Basic reactive store,writable for shared mutable state,Local variables for shared state,const count = writable(0),let count = 0 in module,Medium,https://svelte.dev/docs/svelte-store#writable
21,Stores,Use readable for read-only state,External data sources,readable for derived/external data,writable for read-only data,"readable(0, set => interval(set))",writable(0) for timer,Low,https://svelte.dev/docs/svelte-store#readable
22,Stores,Use derived for computed stores,Combine or transform stores,derived for computed values,Manual subscription for derived,"derived(count, $c => $c * 2)",count.subscribe(c => doubled = c * 2),Medium,https://svelte.dev/docs/svelte-store#derived
23,Stores,Use $ prefix for auto-subscription,Automatic subscribe/unsubscribe,$storeName in components,Manual subscription,{$count},count.subscribe(c => value = c),High,
24,Stores,Clean up custom subscriptions,Unsubscribe when component destroys,Return unsubscribe from onMount,Leave subscriptions open,onMount(() => store.subscribe(fn)),store.subscribe(fn) in script,High,
25,Slots,Use slots for composition,Content projection,<slot> for flexible content,Props for all content,<slot>Default</slot>,"<Component content=""text""/>",Medium,https://svelte.dev/docs/special-elements#slot
26,Slots,Name slots for multiple areas,Multiple content areas,"<slot name=""header"">",Single slot for complex layouts,"<slot name=""header""><slot name=""footer"">",<slot> with complex conditionals,Low,
27,Slots,Check slot content with $$slots,Conditional slot rendering,$$slots.name for conditional rendering,Always render slot wrapper,"{#if $$slots.footer}<slot name=""footer""/>{/if}","<div><slot name=""footer""/></div>",Low,
28,Styling,Use scoped styles by default,Styles scoped to component,<style> for component styles,Global styles for component,:global() only when needed,<style> all global,Medium,https://svelte.dev/docs/svelte-components#style
29,Styling,Use :global() sparingly,Escape scoping when needed,:global for third-party styling,Global for all styles,:global(.external-lib),<style> without scoping,Medium,
30,Styling,Use CSS variables for theming,Dynamic styling,CSS custom properties,Inline styles for themes,"style=""--color: {color}""","style=""color: {color}""",Low,
31,Transitions,Use built-in transitions,Svelte transition directives,transition:fade for simple effects,Manual CSS transitions,<div transition:fade>,<div class:fade={visible}>,Low,https://svelte.dev/docs/element-directives#transition-fn
32,Transitions,Use in: and out: separately,Different enter/exit animations,in:fly out:fade for asymmetric,Same transition for both,<div in:fly out:fade>,<div transition:fly>,Low,
33,Transitions,Add local modifier,Prevent ancestor trigger,transition:fade|local,Global transitions for lists,<div transition:slide|local>,<div transition:slide>,Medium,
34,Actions,Use actions for DOM behavior,Reusable DOM logic,use:action for DOM enhancements,onMount for each usage,<div use:clickOutside>,onMount(() => setupClickOutside(el)),Medium,https://svelte.dev/docs/element-directives#use-action
35,Actions,Return update and destroy,Lifecycle methods for actions,"Return { update, destroy }",Only initial setup,"return { update(params) {}, destroy() {} }",return destroy only,Medium,
36,Actions,Pass parameters to actions,Configure action behavior,use:action={params},Hardcoded action behavior,<div use:tooltip={options}>,<div use:tooltip>,Low,
37,Logic,Use {#if} for conditionals,Template conditionals,{#if} {:else if} {:else},Ternary in expressions,{#if cond}...{:else}...{/if},{cond ? a : b} for complex,Low,https://svelte.dev/docs/logic-blocks#if
38,Logic,Use {#each} for lists,List rendering,{#each} with key,Map in expression,{#each items as item (item.id)},{items.map(i => `<div>${i}</div>`)},Medium,
39,Logic,Always use keys in {#each},Proper list reconciliation,(item.id) for unique key,Index as key or no key,{#each items as item (item.id)},"{#each items as item, i (i)}",High,
40,Logic,Use {#await} for promises,Handle async states,{#await} for loading/error states,Manual promise handling,{#await promise}...{:then}...{:catch},{#if loading}...{#if error},Medium,https://svelte.dev/docs/logic-blocks#await
41,SvelteKit,Use +page.svelte for routes,File-based routing,+page.svelte for route components,Custom routing setup,routes/about/+page.svelte,routes/About.svelte,Medium,https://kit.svelte.dev/docs/routing
42,SvelteKit,Use +page.js for data loading,Load data before render,load function in +page.js,onMount for data fetching,export function load() {},onMount(() => fetchData()),High,https://kit.svelte.dev/docs/load
43,SvelteKit,Use +page.server.js for server-only,Server-side data loading,+page.server.js for sensitive data,+page.js for API keys,+page.server.js with DB access,+page.js with DB access,High,
44,SvelteKit,Use form actions,Server-side form handling,+page.server.js actions,API routes for forms,export const actions = { default },fetch('/api/submit'),Medium,https://kit.svelte.dev/docs/form-actions
45,SvelteKit,Use $app/stores for app state,$page $navigating $updated,$page for current page data,Manual URL parsing,import { page } from '$app/stores',window.location.pathname,Medium,https://kit.svelte.dev/docs/modules#$app-stores
46,Performance,Use {#key} for forced re-render,Reset component state,{#key id} for fresh instance,Manual destroy/create,{#key item.id}<Component/>{/key},on:change={() => component = null},Low,https://svelte.dev/docs/logic-blocks#key
47,Performance,Avoid unnecessary reactivity,Not everything needs $:,$: only for side effects,$: for simple assignments,$: if (x) console.log(x),$: y = x (when y = x works),Low,
48,Performance,Use immutable compiler option,Skip equality checks,immutable: true for large lists,Default for all components,<svelte:options immutable/>,Default without immutable,Low,
49,TypeScript,"Use lang=""ts"" in script",TypeScript support,"<script lang=""ts"">",JavaScript for typed projects,"<script lang=""ts"">",<script> with JSDoc,Medium,https://svelte.dev/docs/typescript
50,TypeScript,Type props with interface,Explicit prop types,interface $$Props for types,Untyped props,interface $$Props { name: string },export let name,Medium,
51,TypeScript,Type events with createEventDispatcher,Type-safe events,createEventDispatcher<Events>(),Untyped dispatch,createEventDispatcher<{ save: Data }>(),createEventDispatcher(),Medium,
52,Accessibility,Use semantic elements,Proper HTML in templates,button nav main appropriately,div for everything,<button on:click>,<div on:click>,High,
53,Accessibility,Add aria to dynamic content,Accessible state changes,aria-live for updates,Silent dynamic updates,"<div aria-live=""polite"">{message}</div>",<div>{message}</div>,Medium,
