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Best Practice

Image Optimization Best Practices

Image optimization uses modern formats, responsive sizing, compression, lazy loading, and CDNs to cut the heaviest bytes on a page. It speeds up LCP and reduces layout shift while keeping images sharp.

Organization
Google (web.dev)
Published
Jan 1, 2019

Best Practice: Image Optimization Best Practices

Images are usually the heaviest part of a web page, often accounting for the majority of transferred bytes, so optimizing them is one of the highest-leverage performance wins available. Image optimization combines modern formats (WebP, AVIF), correct dimensions for each device, sensible compression, lazy loading for offscreen media, and delivery through a CDN that can transform assets on demand. Done well, it cuts bytes dramatically, speeds up Largest Contentful Paint (often the hero image), and reduces cumulative layout shift, all while keeping images visually sharp. The payoff is concrete: faster pages convert better, rank better, and cost less in bandwidth. Google's web.dev guidance is a strong, vendor-neutral reference for the techniques.

Step-by-Step Implementation Guidance

  1. Audit current images for size, format, and dimensions.
  2. Convert photos to AVIF or WebP with appropriate quality settings.
  3. Serve responsive images with srcset and sizes so each device gets the right resolution.
  4. Set explicit width and height to reserve space and prevent layout shift.
  5. Lazy-load offscreen images with the native loading attribute.
  6. Deliver through an image CDN that resizes and compresses on the fly.
  7. Prioritize the LCP image with fetchpriority and avoid lazy-loading it.

Common Mistakes Teams Make When Ignoring This Practice

  • Shipping huge originals scaled down by CSS.
  • Using PNG or JPEG where AVIF or WebP would be far smaller.
  • Omitting width and height, causing cumulative layout shift.
  • Lazy-loading the hero image and delaying LCP.
  • Ignoring art direction and serving one crop to all viewports.

Tools and Techniques That Support This Practice

  • Squoosh, sharp, and ImageMagick for conversion and compression.
  • Image CDNs such as Cloudinary, imgix, and Cloudflare Images.
  • Next.js Image and similar framework components.
  • Lighthouse and WebPageTest for verification.

How This Practice Applies to Different Migration Types

  • Cloud Migration: Move image transformation to an edge CDN for on-the-fly resizing.
  • Database Migration: Store image references, not blobs, and offload binaries to object storage.
  • SaaS Migration: Confirm a new CMS supports modern formats and responsive variants.
  • Codebase Migration: Adopt the new framework's optimized image component during the port.

Checklist

  • Modern formats (AVIF/WebP) used.
  • Responsive srcset and sizes set.
  • Width and height declared.
  • Offscreen images lazy-loaded.
  • LCP image prioritized, not lazy.
  • Delivery via an image CDN.
  • Quality verified against compression.

Category

Frontend

Tags

frontendweb performanceperformance efficiencybest practicescore web vitals
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demo@vibgrate — bash
❯ npx @vibgrate/cli scan
 
╭──────────────────────────────────────────╮
│ Vibgrate Drift Report │
╰──────────────────────────────────────────╯
 
── node-turborepo (node) .
Runtime: >=18.0.0 (6 majors behind)
Frameworks:
Turbo: 1.13.4 → 2.10.12 (1 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Dependencies:
1 current 1 1-behind 3 2+ behind 1 unknown
 
── @repo/admin (node) apps/admin
Frameworks:
TanStack Query: 5.102.5 → 5.102.5 (current)
React: 18.3.1 → 19.2.8 (1 behind)
React DOM: 18.3.1 → 19.2.8 (1 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Vite: 5.4.21 → 8.2.2 (3 behind)
Dependencies:
3 current 9 1-behind 3 2+ behind 4 unknown
 
── @repo/api (node) apps/api
Frameworks:
Express: 4.22.2 → 5.2.1 (1 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Vitest: 1.6.1 → 4.1.11 (3 behind)
Dependencies:
7 current 5 1-behind 3 2+ behind 4 unknown
 
── @repo/web (node) apps/web
Frameworks:
Next.js: 14.2.35 → 16.3.3 (2 behind)
React: 18.3.1 → 19.2.8 (1 behind)
React DOM: 18.3.1 → 19.2.8 (1 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Dependencies:
2 current 6 1-behind 3 2+ behind 5 unknown
 
── @repo/config (node) packages/config
Frameworks:
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Dependencies:
2 current 2 1-behind 5 2+ behind 0 unknown
 
── @repo/database (node) packages/database
Frameworks:
Prisma: 5.22.0 → 7.10.0 (2 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Dependencies:
1 current 0 1-behind 3 2+ behind 1 unknown
 
── @repo/types (node) packages/types
Frameworks:
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Dependencies:
0 current 0 1-behind 1 2+ behind 1 unknown
 
── @repo/ui (node) packages/ui
Frameworks:
React: 18.3.1 → 19.2.8 (1 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
React: 18.3.1 → 19.2.8 (1 behind)
Dependencies:
1 current 4 1-behind 1 2+ behind 1 unknown
 
── @repo/utils (node) packages/utils
Frameworks:
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Vitest: 1.6.1 → 4.1.11 (3 behind)
Dependencies:
0 current 1 1-behind 2 2+ behind 1 unknown
 
Tech Stack
Frontend: React, React DOM
Meta-frameworks: Next.js
Bundlers: tsx, Turbo, Vite
CSS / UI: Autoprefixer, PostCSS, Tailwind CSS
Backend: Express
ORM / Database: Prisma, Prisma Client
Testing: Vitest
Lint & Format: ESLint, ESLint Prettier, ESLint React, Prettier, typescript-eslint
 
Services & Integrations
Auth: JWT 9.0.3
Databases: Prisma 5.22.0
 
TypeScript
v5.3.3 · strict ✔ · MIXED · target: ES2022
 
Build & Deploy
Package Managers: pnpm
Monorepo: npm-workspaces, pnpm-workspaces, turbo
 
Product Purpose Signals
Frameworks: react, nextjs
Evidence: 177
Top Signals:
- [heading] Dashboard (apps/admin/src/pages/Dashboard.tsx)
- [title] Revenue Overview (apps/admin/src/pages/Dashboard.tsx)
- [copy] workspace:* (packages/ui/package.json)
- [copy] ./dist (packages/ui/tsconfig.json)
- [copy] ./src/index.ts (packages/ui/package.json)
- [copy] @repo/config/tsconfig-base.json (packages/ui/tsconfig.json)
- [copy] @repo/ui (packages/ui/package.json)
- [copy] #3b82f6 (apps/admin/src/pages/Dashboard.tsx)
Unknowns:
- No pricing or billing evidence found.
- No integrations/connectors evidence found.
- No route structure evidence found.
 
Security Posture
Lockfile ✖ · .env ✔ · node_modules ✔
 
Platform
Native modules: turbo
 
Code Quality
Files: 36 · Functions: 183 · Avg complexity: 2.62 · Avg length: 21.13 lines
Max nesting: 2 · Circular deps: 0 · Dead code: 0%
God files: apps/admin/src/pages/Products (448 lines)
 
Database Schema
postgresql · 8 models · 1 enum
Models: Address, CartItem, Category, Order, OrderItem (+3 more)
 
Findings (16 errors, 11 warnings)
✖ Node.js runtime ">=18.0.0" reached end-of-life on 2025-04-30 (latest: 24.0.0).
vibgrate/runtime-eol in .
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in .
✖ 60% of dependencies are 2+ major versions behind in node-turborepo.
vibgrate/dependency-rot in .
✖ @types/node is 6 major versions behind (spec: ^20.11.0, latest: 26.3.0).
vibgrate/dependency-major-lag in .
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in apps/admin
✖ Vite is 3 major versions behind (current: 5.4.21, latest: 8.2.2).
vibgrate/framework-major-lag in apps/admin
✖ vite is 3 major versions behind (spec: ^5.0.12, latest: 8.2.2).
vibgrate/dependency-major-lag in apps/admin
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in apps/api
✖ Vitest is 3 major versions behind (current: 1.6.1, latest: 4.1.11).
vibgrate/framework-major-lag in apps/api
✖ @types/node is 6 major versions behind (spec: ^20.11.0, latest: 26.3.0).
vibgrate/dependency-major-lag in apps/api
✖ vitest is 3 major versions behind (spec: ^1.2.1, latest: 4.1.11).
vibgrate/dependency-major-lag in apps/api
⚠ Next.js is 2 major versions behind (current: 14.2.35, latest: 16.3.3).
vibgrate/framework-major-lag in apps/web
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in apps/web
✖ @types/node is 6 major versions behind (spec: ^20.11.0, latest: 26.3.0).
vibgrate/dependency-major-lag in apps/web
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in packages/config
✖ 56% of dependencies are 2+ major versions behind in @repo/config.
vibgrate/dependency-rot in packages/config
✖ eslint-plugin-react-hooks is 3 major versions behind (spec: ^4.6.0, latest: 7.1.1).
vibgrate/dependency-major-lag in packages/config
⚠ Prisma is 2 major versions behind (current: 5.22.0, latest: 7.10.0).
vibgrate/framework-major-lag in packages/database
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in packages/database
✖ 75% of dependencies are 2+ major versions behind in @repo/database.
vibgrate/dependency-rot in packages/database
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in packages/types
✖ 100% of dependencies are 2+ major versions behind in @repo/types.
vibgrate/dependency-rot in packages/types
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in packages/ui
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in packages/utils
✖ Vitest is 3 major versions behind (current: 1.6.1, latest: 4.1.11).
vibgrate/framework-major-lag in packages/utils
✖ 67% of dependencies are 2+ major versions behind in @repo/utils.
vibgrate/dependency-rot in packages/utils
✖ vitest is 3 major versions behind (spec: ^1.2.1, latest: 4.1.11).
vibgrate/dependency-major-lag in packages/utils
 
╭──────────────────────────────────────────╮
│ Top Priority Actions │
╰──────────────────────────────────────────╯
 
1. Upgrade EOL runtime in node-turborepo
End-of-life runtimes no longer receive security patches and block ecosystem upgrades.
./.
>=18.0.0 → 24.0.0 (6 majors behind)
Impact: −10 drift points (runtime & EOL)
 
2. Fix security posture: no lockfile found
Without a lockfile, installs are non-deterministic. Run the install command to generate one and commit it.
./
Missing: package-lock.json, pnpm-lock.yaml, or yarn.lock
 
3. Upgrade Vite 5.4.21 → 8.2.2 in @repo/admin (+2 more)
3 major versions behind. Major framework drift increases breaking change risk and blocks access to security fixes and performance improvements.
./apps/admin
Vite: 5.4.21 → 8.2.2 (3 majors behind)
./apps/api
Vitest: 1.6.1 → 4.1.11 (3 majors behind)
./packages/utils
Vitest: 1.6.1 → 4.1.11 (3 majors behind)
Impact: −5–15 drift points
 
4. Reduce dependency rot in @repo/types (100% severely outdated)
1 of 1 dependencies are 2+ majors behind. Run `npm outdated` and prioritise packages with known CVEs or breaking API changes.
./packages/types
typescript: 5.9.3 → 7.0.2 (2 majors behind)
Impact: −5–10 drift points
 
5. Reduce dependency rot in @repo/database (75% severely outdated)
3 of 4 dependencies are 2+ majors behind. Run `npm outdated` and prioritise packages with known CVEs or breaking API changes.
./packages/database
@prisma/client: 5.22.0 → 7.10.0 (2 majors behind)
prisma: 5.22.0 → 7.10.0 (2 majors behind)
typescript: 5.9.3 → 7.0.2 (2 majors behind)
Impact: −5–10 drift points
 
╭──────────────────────────────────────────╮
│ Architecture Layers │
╰──────────────────────────────────────────╯
 
Archetype: nextjs (80% confidence)
Files classified: 24 (11 unclassified)
Folders classified: 8
apps/admin/src presentation 100% 4 files
apps/admin/src/pages presentation 100% 2 files
apps/api/src/middleware middleware 100% 2 files
apps/api/src/routes routing 100% 2 files
apps/web/src/app presentation 100% 4 files
apps/web/src/app/products presentation 100% 2 files
apps/web/src/app/products/[id] presentation 100% 1 file
packages/ui/src presentation 100% 6 files
Unclassified source (sample): 11
 
presentation 15 files drift ████████████████████ 100 risk high
routing 4 files drift ████████████████████ 100 risk high
middleware 2 files drift ███████▍░░░░░░░░░░░░ 37 risk moderate
config 2 files drift ░░░░░░░░░░░░░░░░░░░░ 0 risk none
shared 1 file drift ████████████████████ 100 risk high
 
╭──────────────────────────────────────────╮
│ DriftScore Summary │
╰──────────────────────────────────────────╯
 
DriftScore: 66/100
Risk Level: HIGH
Projects: 9
Classified: 8 nano · 1 micro · 0 small · 0 standard
Billable: 0.42 · 9 detected → 0.42 billable projects (micro-project pricing)
0.1 micro · 0.32 nano
These fractions add up across repositories, then round down to whole billable projects.
 
Score Breakdown
Runtime: ████████████████████ 100
Frameworks: █████████▏░░░░░░░░░░ 46
Dependencies: ██████▏░░░░░░░░░░░░░ 31
EOL Risk: ████████████████████ 100
 
Scanned at 2026-08-26T09:08:28.481Z · 7.1s · 286 files scanned · 56 workspace files · 27 dirs
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