The key is testing like a detective, not a tourist. Start with this guide to how to test load time for a website :

1. Baseline with Real User Monitoring (RUM): Tools like Cloudflare Radar or Freshpaint track actual visitor experiences across devices/locations. This exposes real-world issues (e.g., slow 3G mobile users in rural areas).

2. Synthetic Testing for Root Causes: Use WebPageTest.org from multiple global nodes (Virginia, Mumbai, São Paulo). Check “filmstrip view” to see how content loads sequentially. For dynamic sites, script a logged-in user journey (e.g., add to cart → checkout) using Puppeteer or Playwright.

3. Decode Server-Side Slowness: Tools like DebugBear isolate backend delays. If TTFB (Time to First Byte) is high, your host or database is the culprit. We found a 4s TTFB due to unindexed SQL queries—fixed it without touching the frontend.

4. Prioritize Critical Issues: Lighthouse’s “opportunities” can be paralyzing. Filter by impact: Focus on “Largest Contentful Paint” (optimize images/CDN) and “Total Blocking Time” (defer non-critical JS).