Why speed matters
Half of all people close a website that takes longer than 3 seconds to load. Your visitors won’t all have a brand-new phone on fast Wi-Fi – some will have an older phone on a train. A project boss thinks about them too.
Good news: you can get the biggest speed boost from just one thing – images. A photo straight from a phone can easily be 5 MB; a website only needs a tenth of that.
Show me: measure with Lighthouse
Lighthouse is a measuring tool built right into Chrome:
- Open your website (the live version, not localhost).
- F12 → Lighthouse tab → Analyze page load.
- You’ll get a score from 0–100 for performance, accessibility, SEO – and most importantly, a list of specific tips on what to improve.
The most common tips and what to do about them:
| Lighthouse tip | What to do |
|---|---|
| Properly size images | shrink your images (see below) |
| Serve images in next-gen formats | save them as WebP |
| Image elements do not have width/height | add width and height attributes |
| Links do not have descriptive text | instead of “click here”, say where the link goes |
Shrink your images
- Dimensions: a website only needs about 1200px width (a hero photo) or about 600px (a regular photo). You can resize in any editor, even online (e.g. squoosh.app).
- Format: WebP is about a third smaller than JPG at the same quality.
- Lazy loading: images below the fold only load once the visitor scrolls down to them:
<img src="photo.webp" alt="Match against the Eagles" width="600" height="400" loading="lazy" />Now it’s your turn 💪
- Measure your website with Lighthouse and write down your performance score – that’s your starting line.
- Find the 3 largest images on your website (F12 → Network tab → sort by Size).
- Shrink them (dimensions + WebP) and add
loading="lazy"to everything except the first image at the top. - Measure again and compare scores. Write in
LAUNCH.md: before → after. - Bonus: test your website on your phone with Wi-Fi turned off. What’s it like?
Don’t expect 100 points. Even big websites score 70–90. What matters is progress: going from 60 to 85 is a win that visitors will actually notice.
Check: You know your Lighthouse score before and after. Your images are resized, in WebP, and using lazy loading. Your website noticeably loads faster on mobile.
What to take away from this lesson
- Speed = visitors stay. 3 seconds is the limit.
- Lighthouse tells you exactly what to improve.
- The biggest lever: smaller images (dimensions, WebP, lazy loading).
© 2026 Ing. Martin Polak / AlgoRhino · Content usage terms