vercel-performance-tuning

Optimize Vercel deployment performance with caching, bundle optimization, and cold start reduction. Use when experiencing slow page loads, optimizing Core Web Vitals, or reducing serverless function cold start times. Trigger with phrases like "vercel performance", "optimize vercel", "vercel latency", "vercel caching", "vercel slow", "vercel cold start".

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Repository: jeremylongshore/tons-of-skills-marketplace
Last source activity: August 19, 2026 at 12:13
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name	vercel-performance-tuning
description	Optimize Vercel deployment performance with caching, bundle optimization, and cold start reduction. Use when experiencing slow page loads, optimizing Core Web Vitals, or reducing serverless function cold start times. Trigger with phrases like "vercel performance", "optimize vercel", "vercel latency", "vercel caching", "vercel slow", "vercel cold start".
allowed-tools	Read, Write, Edit, Bash(vercel:), Bash(npx:)
version	1.18.0
license	MIT
author	Jeremy Longshore <jeremy@intentsolutions.io>
tags	["saas","vercel","performance","caching","optimization"]
compatibility	Designed for Claude Code

Vercel Performance Tuning

Overview

Optimize Vercel deployment performance across four levers: edge caching, bundle size reduction, serverless function cold start elimination, and Core Web Vitals improvement. Uses real Vercel cache headers, ISR, and Edge Functions for maximum performance.

Prerequisites

Vercel project deployed with accessible URL
Access to Vercel Analytics (dashboard)
Bundle analyzer available (@next/bundle-analyzer or similar)

Instructions

Step 1: Establish Performance Baseline

# Check deployment size and function count
vercel inspect https://my-app.vercel.app

# Run Lighthouse via CLI
npx lighthouse https://my-app.vercel.app --output=json --quiet \
  | jq '{performance: .categories.performance.score, lcp: .audits["largest-contentful-paint"].numericValue, cls: .audits["cumulative-layout-shift"].numericValue}'

# Check bundle size (Next.js)
ANALYZE=true npx next build
# Opens bundle analyzer report in browser

Enable Vercel Analytics in the dashboard under Analytics tab for ongoing monitoring.

Step 2: Configure Edge Caching

// api/cached-data.ts — cache API responses at the edge
import type { VercelRequest, VercelResponse } from '@vercel/node';

export default function handler(req: VercelRequest, res: VercelResponse) {
  // Cache at Vercel edge for 60s, serve stale for 300s while revalidating
  res.setHeader('Cache-Control', 's-maxage=60, stale-while-revalidate=300');
  res.json({ data: (), :  ().() });
}

// vercel.json — cache static assets aggressively
{
  "headers": [
    {
      "source": "/static/(.*)",
      "headers": [
        { "key": "Cache-Control", "value": "public, max-age=31536000, immutable" }
      ]
    },
    {
      "source": "/api/public-data",
      "headers": [
        { "key": "Cache-Control", "value": "s-maxage=3600, stale-while-revalidate=86400" }
      ]
    }
  ]
}

Header	Effect
`s-maxage=N`	Cache at Vercel edge for N seconds
`stale-while-revalidate=N`	Serve stale while revalidating in background
`max-age=N`	Cache in browser for N seconds
`immutable`	Never revalidate (use with content-hashed filenames)
`no-cache`	Always revalidate (edge still caches)
`no-store`	Never cache anywhere

// app/products/[id]/page.tsx (Next.js App Router)
export const revalidate = 60; // Revalidate every 60 seconds

export default async function ProductPage({ params }) {
  const product = await fetchProduct(params.id);
  return <ProductView product={product} />;
}

// Generate static pages at build time, regenerate on-demand
export async function generateStaticParams() {
  const products = await fetchTopProducts(100);
  return products.map(p => ({ id: p.id }));
}

// api/revalidate.ts
import type { VercelRequest, VercelResponse } from '@vercel/node';

export default async function handler(req: VercelRequest, res: VercelResponse) {
  const secret = req.query.secret;
  if (secret !== process.env.REVALIDATION_SECRET) {
    return res.status(401).json({ error: 'Invalid secret' });
  }

  const path = req.query.path as string;
  await res.revalidate(path);
  res.json({ revalidated: true, path });
}
// Trigger: POST /api/revalidate?secret=xxx&path=/products/123

// Lazy initialization — don't import heavy modules at top level
// BAD: Cold start loads everything
import { PrismaClient } from '@prisma/client';
const prisma = new PrismaClient(); // Runs on every cold start

// GOOD: Lazy singleton — only connects when first used
let prisma: PrismaClient | null = null;
function getDb(): PrismaClient {
  if (!prisma) {
    prisma = new PrismaClient();
  }
  return prisma;
}

export default async function handler(req, res) {
  const users = await getDb().user.findMany();
  res.json(users);
}

// api/fast.ts
export const config = { runtime: 'edge' };

export default function handler(request: Request) {
  return Response.json({ fast: true }); // No cold start, runs globally
}

// next.config.js — tree-shaking and optimization
module.exports = {
  experimental: {
    optimizePackageImports: ['lodash', '@mui/material', '@mui/icons-material'],
  },
  // Exclude server-only deps from client bundle
  webpack: (config, { isServer }) => {
    if (!isServer) {
      config.resolve.fallback = { fs: false, net: false, tls: false };
    }
    return config;
  },
};

# Find large dependencies
npx depcheck
npx cost-of-modules

# Replace heavy libraries with lighter alternatives
# moment.js (300KB) → dayjs (2KB)
# lodash (72KB) → lodash-es with tree-shaking
# axios (29KB) → native fetch

// Use Vercel's built-in image optimization
import Image from 'next/image';

// Automatic: resizes, converts to WebP/AVIF, caches at edge
<Image
  src="/hero.jpg"
  width={1200}
  height={600}
  alt="Hero"
  priority  // Preload for LCP
  sizes="(max-width: 768px) 100vw, 1200px"
/>

// vercel.json — configure image optimization
{
  "images": {
    "sizes": [640, 750, 828, 1080, 1200],
    "domains": ["images.example.com"],
    "formats": ["image/avif", "image/webp"],
    "minimumCacheTTL": 86400
  }
}

Metric	Target	Vercel Tool
LCP	< 2.5s	Vercel Analytics
FID/INP	< 200ms	Vercel Analytics
CLS	< 0.1	Vercel Analytics
TTFB	< 200ms	Edge caching
Function cold start	< 500ms	Lazy init / Edge Functions
Bundle size (gzipped)	< 200KB JS	Bundle analyzer

Error	Cause	Solution
Cache not hitting	Missing `s-maxage` header	Add to response or vercel.json headers
ISR page always stale	`revalidate` set too high	Lower the revalidation interval
Large bundle warning	Importing entire library	Use specific imports: `import { map } from 'lodash-es'`
Cold start > 1s	Heavy top-level imports	Move to lazy initialization pattern
Images not optimized	External domain not whitelisted	Add to `images.domains` in config