A set of standards for applications built with Next.js 16’s App Router, which organizes pages and layouts using the framework’s newer routing system. It specifies where server and client code, business logic, mutations, translations, metadata, loading states, and security checks belong.

Use them when building or reviewing Next.js routes, server and client components, server actions, translations, SEO metadata, loading states, and request-security checks.

Without boundaries, page files can accumulate business logic, browser-only code, database access, and security-sensitive operations. These rules keep those responsibilities in predictable places.

nextjs — Cursor rule by virastack

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add rules/virastack/ai/nextjs

Clone the repo

git clone --depth 1 https://github.com/virastack/ai

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.

When invoked 1,230 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5	$0.00000	$0.01230
Opus 5	$0.00000	$0.00615
Sonnet 5	$0.00000	$0.00246
Haiku 4.5	$0.00000	$0.00123

Measured yesterday against content hash 969c194e830a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

nextjs scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

templates/nextjs/.cursor/rules/nextjs.mdc · 151 lines

How it starts

The opening of the file, as written. The whole thing — 151 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Next.js 16 App Router Constitution

Constraints

Server-First Architecture: All components in src/app MUST be Server Components (RSC) by default.
Client Component Usage: The "use client" directive is strictly limited to leaf-node components that require interactivity (hooks, events) or Browser APIs.
Feature Delegation: src/app is strictly for routing/layout. All business logic, UI components, and domain hooks MUST reside in src/features.
Server Actions: All mutations MUST use Server Actions defined in dedicated actions.ts files within src/features. Actions MUST call the API layer only; direct database access inside actions is forbidden.
i18n Implementation: Use next-intl for translations. Follow the patterns defined in i18n.mdc.
Metadata: SEO metadata MUST be defined using the Metadata API in page.tsx or layout.tsx.
Streaming: Use loading.tsx for route-level async states. Use <Suspense> for granular feature-level hydration.
CSRF Protection: Verify Origin/Referer headers in Server Actions. Use action.bind to lock sensitive IDs on the server-side.
Secret Isolation: Use the server-only package in API and database files to prevent accidental leakage to the client.

Bans

Inline Server Actions: Defining Server Actions inside components or pages is FORBIDDEN.
Client-Side Data Fetching in Effects: Using useEffect for data fetching is FORBIDDEN. Use TanStack Query or RSC.
Logic in Route Files: Implementing complex logic directly in page.tsx or layout.tsx is FORBIDDEN.
Manual Head Management: Using head.tsx or manual <meta> tags is FORBIDDEN.
"use client" at Root: Marking page.tsx or layout.tsx as "use client" is FORBIDDEN. Wrap interactive logic in feature components instead.
Raw Serialization: Forbidden to pass raw database models or sensitive user data directly from RSC to Client Components.

Mandatory Patterns

1. Assets & Performance (Next.js Specifics)

Use Next.js built-in optimizations for assets.

ALWAYS use next/image for images to ensure automatic WebP/AVIF optimization and resizing.
ALWAYS use next/font for fonts to prevent layout shift (CLS).
ALWAYS use next/script for third-party scripts to unblock the main thread.
Use next/dynamic for heavy client-side components that are not immediately visible.

Read the full file on GitHub · 151 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

yesterday First seen · 151 lines · 0 tokens per session scan A 969c194e830a

Subscribe to this mod's changes

nextjs is a cursor rule published in the GitHub repository virastack/ai (23 stars, last pushed 25d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 1,230 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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nextjs