Why is my application slow? The 3 most frequent causes

A slow application drives users away long before they read your text. The good news: the cause is often one of the three below.

1. Images that are too heavy

A 5 MB photo displayed in a 300-pixel frame is the most common mistake. The browser downloads everything, then shrinks it. Compressing and resizing images is often enough to divide the loading time.

2. Too many database requests

A page that shows 50 items and makes one request per item makes 50 round trips, when a single well-written request could bring everything back. It is invisible with 10 test records, and very visible with 10,000 real ones.

3. Code loaded "just in case"

Many applications send all their code to the browser on the first page, including screens the user may never see. Loading only what is needed first lightens the start.

How to know which one affects you

1. Open your application in Chrome and run a "Lighthouse" test: it lists what slows the page down.
2. Look at the weight of images and the number of requests.
3. Test with a lot of data, not just three rows.

Measure first, fix afterwards: without measurement, you often optimise the wrong part.