How do their APIs compare?

I need more specificity to give you a useful comparison. "APIs" is very broad across two large frameworks.

sveltejs/kit and vercel/next.js are both full-stack web frameworks, but they have fundamentally different design philosophies:

• SvelteKit is built on Vite, uses Svelte components, and organizes code around file-based routing with +page.svelte, +server.js, +layout.svelte conventions.
• Next.js uses webpack (with Turbopack as an option), React/JSX, and organizes around page.tsx/route.ts in the App Router.

To give you a meaningful comparison, I'd need to know which specific APIs interest you:

• Routing (file structure, dynamic segments, error handling)?
• Server-side hooks (like sequence() in SvelteKit vs Next.js middleware)?
• Data loading (load functions vs getServerSideProps/getStaticProps)?
• Environment/config (svelte.config.js vs next.config.js)?
• Request/response handling (headers, cookies, body parsing)?
• Build/deployment adapters?

Pick one or more areas and I can pull concrete examples with file citations.

FOLLOW_UPS:

• How do SvelteKit and Next.js handle routing?
• What are SvelteKit's load functions vs Next.js data fetching?
• How do server hooks differ between the two frameworks?

Based on the repository data and search results, here's how SvelteKit and Next.js differ in routing:

SvelteKit Routing

File-based structure with + prefix convention:

• Pages: +page.svelte (pages) / +page.server.js (server-only)
• Layouts: +layout.svelte / +layout.server.js
• API endpoints: +server.js
• Error boundaries: +error.svelte

Dynamic segments use brackets:

• [param] — required parameter
• [[optional]] — optional parameter
• [...rest] — rest/catch-all parameter
• [file].[ext] — multiple parameters in one segment

SvelteKit has a sophisticated route sorting algorithm [packages/kit/src/core/sync/create_manifest_data/sort.js:L18-L134] that prioritizes specificity: static segments rank highest, then required parameters, optional parameters, and rest parameters lowest. Named layouts with @ syntax (e.g., +layout@special.svelte) allow breaking out of the layout hierarchy.

Validation is strict [packages/kit/src/core/sync/create_manifest_data/index.js:L165-L204]:

• Parameters must be separated ([foo][bar] throws an error)
• Brackets must be balanced
• [[optional]] cannot follow [...rest]

Next.js Routing (App Router)

From the repository data provided, I can see Next.js has CLI commands for routing analysis [packages/next/src/bin/next.ts:L742-L772], including options like --sort and filtering, but the complete App Router file structure isn't fully detailed in the provided chunks.

However, conceptually, Next.js uses:

• page.tsx (pages) / route.ts (API endpoints)
• layout.tsx (layouts)
• [param], [[...params]], (...group) syntax for dynamic/grouped routes

Key Differences

Aspect	SvelteKit	Next.js
File prefix	+page, +layout, +server	page, layout, route
Endpoint handling	+server.js (flexible methods)	route.ts (export GET, POST, etc.)
Route validation	Strict bracket rules [L165-L204]	More permissive
Optional segments	[[param]] with double brackets	[[...params]] catch-all style
Named layouts	+layout@name.svelte explicit targeting	Implicit hierarchy

FOLLOW_UPS:

• How do SvelteKit's load functions work with routing?
• What are SvelteKit's endpoint handlers and how do they differ?
• How does named layout targeting work in SvelteKit?