server-vs-client-components

A set of rules for deciding whether a Next.js component should run on the server or in the browser. Server Components are the default; interactive code using state, effects, event handlers, or browser features belongs in a small Client Component.

In plain words
What is it for?
Use it when designing or reviewing Next.js component boundaries, especially data fetching, layouts, forms, buttons, dropdowns, and other interactive elements.
Why use it?
It helps avoid sending unnecessary code to the browser and prevents server-only work from being moved into interactive components. The result is a clearer separation between data work and browser interaction.

Cursor rule for Cursor

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/vibestackdev/vibe-stack/server-vs-client-components
Clone the repo
git clone --depth 1 https://github.com/vibestackdev/vibe-stack

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 249 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.

ModelPer sessionOnce invoked
Fable 5 $0.00000 $0.00249
Opus 5 $0.00000 $0.00125
Sonnet 5 $0.00000 $0.00050
Haiku 4.5 $0.00000 $0.00025

Measured yesterday against content hash 6f7ddaee8557, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

server-vs-client-components 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.

.cursor/rules/server-vs-client-components.mdc · 35 lines

What it actually says

Server vs Client Components

Decision Tree (ALWAYS follow this order):

  1. Can this component run as a Server Component? DEFAULT: YES
  2. Does it use: useState, useEffect, useRef, event handlers, or browser APIs? → ONLY THEN add 'use client'
  3. Push 'use client' to the smallest possible LEAF component

Optimization pattern:

  • Server Component: data fetching, layout, most of the tree
  • Client Component: only the interactive parts (button, form input, dropdown)

❌ Anti-pattern (Avoid):

'use client'  
export default function ProductPage({ id }) {
  // Uses server fetch — should be Server Component
  const [product, setProduct] = useState(null)
  useEffect(() => { fetch(`/api/products/${id}`).then(...) }, [])
}

✅ Correct:

// Server Component — no 'use client' needed for data fetching
export default async function ProductPage({ id }) {
  const product = await getProduct(id) 
}
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.

  1. yesterday First seen · 35 lines · 0 tokens per session scan A 6f7ddaee8557

Subscribe to this mod's changes

server-vs-client-components is a cursor rule published in the GitHub repository vibestackdev/vibe-stack (7 stars, last pushed 2d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 249 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 2026-08-31.