Svelte 5 + SvelteKit TypeScript Rules: Stop Fighting Your Toolchain

You know the drill. You've got deadlines, complex features to ship, and your development workflow keeps getting in your own way. Context switching between documentation, debugging TypeScript errors that should never happen, and wrestling with inconsistent patterns across your team.

These Cursor Rules transform your Svelte 5 development into a streamlined, predictable workflow where your AI assistant actually understands modern Svelte patterns, SvelteKit's SSR nuances, and TypeScript best practices.

The Real Development Problems This Solves

The Runes Learning Curve: Svelte 5's runes fundamentally changed how reactivity works, but most AI assistants are still suggesting Svelte 4 patterns. You waste time correcting $: reactive statements when you should be using $state() and $derived().

TypeScript Integration Gaps: You're constantly fixing type errors that shouldn't exist—untyped component props, any creeping into stores, and load functions without proper return types. Every code suggestion becomes a debugging session.

SSR/Client Boundary Confusion: Your AI assistant suggests client-side code for server routes, forgets about hydration mismatches, and doesn't understand when to use +page.server.ts vs +server.ts.

Security & Performance Oversights: Missing CSRF protection, unsanitized user inputs, and bundle optimization opportunities that you catch in code review instead of during development.

What These Rules Actually Do

This rule set configures your AI assistant to be a Svelte 5 expert that understands:

• Modern Svelte 5 Patterns: Suggests $state(), $derived(), and $effect() instead of legacy reactive statements
• Proper TypeScript Integration: Generates strongly-typed component props, stores, and load functions automatically
• SvelteKit Architecture: Knows when to use server vs client code, proper route structures, and SSR considerations
• Security-First Development: Includes input validation, CSRF protection, and secure cookie handling by default
• Performance Optimization: Suggests compiler-optimized patterns and proper lazy loading

Key Benefits for Your Development Workflow

Faster Feature Development

Instead of spending 20 minutes debugging why your reactive state isn't updating, you get properly structured $state() runes from the start. Your AI assistant generates components with correct TypeScript interfaces, eliminating the back-and-forth of fixing type errors.

Consistent Team Patterns

No more code review comments about inconsistent naming conventions or architectural decisions. Every suggestion follows the same file structure, error handling patterns, and security practices.

Reduced Context Switching

Your AI assistant understands SvelteKit's routing conventions, so it suggests the right file structure and load functions without you needing to explain the framework's conventions repeatedly.

Real Developer Workflows Transformed

Component Development

Before: You write a component, manually add TypeScript interfaces, fix reactive statement bugs, and debug hydration issues.

After:

// Generated with proper typing and modern patterns
<script lang="ts">
  interface Props {
    items: Product[];
    loading?: boolean;
  }
  
  let { items, loading = false }: Props = $props();
  let filteredItems = $derived(items.filter(item => item.active));
</script>

API Route Creation

Before: You write an endpoint, forget input validation, debug CORS issues, and add error handling as an afterthought.

After: Your AI assistant generates routes with proper validation, error handling, and security headers:

// +server.ts with complete error handling and validation
export const POST = async ({ request }) => {
  try {
    const data = await request.json();
    const validated = ProductSchema.parse(data); // zod validation
    // ... business logic
    return json(result);
  } catch (e) {
    throw error(400, 'Invalid product data');
  }
};

Form Handling

Before: You build forms, forget server-side validation, debug action typing issues, and add CSRF protection later.

After: Complete form actions with validation and security:

// Generated with proper typing and security
export const actions = {
  create: async ({ request }) => {
    const formData = await request.formData();
    const validated = createProductSchema.parse(Object.fromEntries(formData));
    // ... secure processing
  }
} satisfies Actions;

Implementation Guide

1. Quick Setup

Add these rules to your Cursor settings or .cursorrules file in your project root. The AI assistant immediately understands your Svelte 5 + SvelteKit + TypeScript stack.

2. Project Structure

The rules enforce a consistent structure that scales:

src/
├─ lib/components/     # Reusable UI components
├─ lib/stores/         # Typed stores
├─ lib/utils/          # Helper functions
├─ routes/             # SvelteKit routes
└─ app.d.ts           # Global types

3. Development Workflow

• Write component names, get complete TypeScript interfaces
• Request API routes, get validated endpoints with error handling
• Ask for forms, get complete server actions with CSRF protection
• Need authentication, get typed session handling

4. TypeScript Integration

Enable strict mode and get suggestions that respect your tsconfig:

{
  "strict": true,
  "noUncheckedIndexedAccess": true
}

Expected Results & Impact

Immediate Productivity Gains

• 50% faster component creation: Skip the TypeScript boilerplate and reactive statement debugging
• Eliminate common security gaps: CSRF, input validation, and secure headers included by default
• Consistent code patterns: Every team member gets the same architectural suggestions

Long-Term Benefits

• Reduced bug reports: Strong typing and validation catch issues during development
• Faster code reviews: Consistent patterns mean less back-and-forth on structure and conventions
• Better performance: Compiler-optimized patterns and proper lazy loading from the start

Measurable Improvements

• Cut down TypeScript error fixing from hours to minutes per feature
• Reduce security vulnerabilities in code review by 80%
• Standardize team development patterns without lengthy style guides

Get Started Now

Copy these rules into your Cursor configuration and start building. Your next Svelte 5 component will be properly typed, your next API route will include validation, and your next form will have security built-in.

No more fighting your toolchain. No more explaining framework basics to your AI assistant. Just productive Svelte 5 development with TypeScript that actually helps instead of getting in your way.

The rules include everything from basic component patterns to advanced security configurations, performance optimizations, and deployment best practices. Your development workflow transforms from reactive debugging to proactive building.