Measuring before you optimise

Guessing why a site is slow wastes days. Measure first, then fix the biggest cost.

Split the request into parts

A page load has three distinct costs:

• Time to first byte (TTFB): how long the server takes to answer. Mostly code and database.
• Download: page weight, image sizes, compression.
• Rendering: scripts and styles the browser must process.

Measure TTFB from the command line:

curl -o /dev/null -s -w "%{time_starttransfer}\n" https://yourcompany.com/

Above 0.6 seconds usually means server-side work is the problem.

Find the slow part on the server

• Enable the database slow query log (long_query_time = 1) and read it after a busy day.
• Check PHP-FPM's status page for workers that are all busy.
• Watch top during peak hours: is it CPU, memory (swap use), or disk wait (wa)?

Front-end checks

Run Lighthouse or PageSpeed Insights and focus on Largest Contentful Paint. The usual fixes are resizing images, serving WebP/AVIF, and deferring scripts that aren't needed at first paint.