Core Web Vitals (LCP, INP, CLS) & Lighthouse 100 Audit Skill

Audit and optimize website loading and interaction performance: eliminate render-blocking CSS/JS, preload LCP hero assets, prevent layout shifts, and reduc

---
name: web-perf
description: Audit and optimize website loading and interaction performance: eliminate render-blocking CSS/JS, preload LCP hero assets, prevent layout shifts, and reduce main-thread TBT. Use when working with Core Web Vitals, Lighthouse, LCP / INP / CLS, Web Performance.
triggers:
  - web perf
  - core web vitals
  - lighthouse
---

# Core Web Vitals (LCP, INP, CLS) & Lighthouse 100 Audit Skill

## 1. When to Use This Skill
Load `skill-web-perf` whenever an engineering or operations task involves **Core Web Vitals, Lighthouse, LCP / INP / CLS, Web Performance**. Specifically:
- Audit and optimize website loading and interaction performance: eliminate render-blocking CSS/JS, preload LCP hero assets, prevent layout shifts, and reduce main-thread TBT.
- Designing, reviewing, or debugging production configurations without guesswork or deprecated flags.
- Running deterministic pre-flight and post-execution verification checks before reporting completion.

## 2. Prerequisites & Required Environment
- **Target Stack:** Core Web Vitals, Lighthouse, LCP / INP / CLS, Web Performance
- **Permissions:** Read-only inspection by default; ask for explicit confirmation before executing destructive mutations or production deployments.
- **Reference Repository:** `https://github.com/GoogleChrome/lighthouse`

## 3. Step-by-Step Execution Playbook
1. **Context & Configuration Discovery:**
   Inspect existing project manifests (`package.json`, `wrangler.jsonc`, schema files, or environment declarations) before proposing changes. Never overwrite existing bindings or credentials blindly.
2. **Deterministic Implementation:**
   Apply the canonical patterns for **Core Web Vitals**:
   - Enforce strict schema/type validation at every external boundary.
   - Include explicit error handling, structured logging, and idempotency keys on all mutating calls.
   - Keep secrets in environment variables or secret stores—never hardcode tokens in source files.
3. **Verification & Regression Gate:**
   Run the verification commands below and inspect both exit codes and output payloads before marking the task complete.

## 4. Reference Commands & CLI Workflow
```bash
npx lighthouse https://example.com --output=json --chrome-flags='--headless'
```

## 5. Edge Cases & Anti-Hallucination Guardrails
- **Zero Unverified Claims:** Never claim a deployment, migration, or API call succeeded without inspecting the command output or HTTP status code.
- **Rollback Readiness:** Always record the previous state or migration version so changes can be reverted cleanly if downstream health checks fail.

Synthesized Engineering Blueprint & Setup Guide