Performance Optimization

# Performance Optimization

## Overview

Measure before optimizing. Performance work without measurement is guessing — and guessing leads to premature optimization that adds complexity without improving what matters. Profile first, identify the actual bottleneck, fix it, measure again. Optimize only what measurements prove matters.

## When to Use

- Performance requirements exist in the spec (load time budgets, response time SLAs)
- Users or monitoring report slow behavior
- Core Web Vitals scores are below thresholds
- You suspect a change introduced a regression
- Building features that handle large datasets or high traffic

**When NOT to use:** Don't optimize before you have evidence of a problem. Premature optimization adds complexity that costs more than the performance it gains.

## Core Web Vitals Targets

| Metric | Good | Needs Improvement | Poor |
|--------|------|-------------------|------|
| **LCP** (Largest Contentful Paint) | ≤ 2.5s | ≤ 4.0s | > 4.0s |
| **INP** (Interaction to Next Paint) | ≤ 200ms | ≤ 500ms | > 500ms |
| **CLS** (Cumulative Layout Shift) | ≤ 0.1 | ≤ 0.25 | > 0.25 |

## The Optimization Workflow