November 14, 2019
How to get a 100% Google Lighthouse score

Google will soon shame slow websites. A good reason to take a good look at your Google Lighthouse score right now.

You might feel that it is nearly impossible to get to a perfect 100% score. You minified your Javascript, properly scaled your images and even combined some requests, but that did not help nearly enough. The problem is: you might be looking at it from the wrong angle.

I build 100% scoring websites on a daily basis, so obviously it is very well possible to get a perfect score on all your websites with little effort. I will try to explain what we want to achieve and how we can achieve that.

There are some basic facts that a lot of people get wrong when it comes to speed and performance. Minifying does not beat gzipping, image scaling does not beat JPG compression and combining requests is actually counter-effective over HTTP/2. These are probably the reasons why your earlier efforts had so little effect. Another important thing to know is that Google Lighthouse simulates a slow connection. This emphasizes the importance of a low ‘page weight’ or ’total size’ over fast infrastructure, as a small page is delivered significantly faster over such a narrow connection than a large page.

Before we look at the actual steps we need to take, let us look at some websites that score (nearly) 100 points on all four categories. It will give you an idea of what the end-result could or should look like. For each site I have listed the weights: the Javascript, CSS and the total page weight. You can also see the number of requests, as well as the time it takes the server to respond (TTFB) and the site to load. Note that these results are results from my computer. Finally, I listed the host, the company that built the website and the Google Lighthouse score. Note that the comma separated numbers stand for Performance, Accessibility, Best Practises and SEO.

Javascript: 0kb
CSS: 9kb
Total size: 120kb
Requests: 9
TTFB: 22ms
DOM loaded:     274ms
Loading time: 596ms
Hosted on: CloudFlare (CDN)
Built by: Usecue BV
Score: 99,100,100,100

Javascript: 1kb
CSS: 14kb
Total size: 115kb
Requests: 9
TTFB: 16ms
DOM loaded:     307ms
Loading time: 564ms
Hosted at: CloudFlare (CDN)
Built by: Usecue BV
Score: 100,100,100,100

Javascript: 10kb
CSS: 12kb
Total size: 44kb
Requests: 7
TTFB: 15ms
DOM loaded:     231ms
Loading time: 363ms
Hosted at: Leaseweb (VM)
Built by: Usecue BV
Score: 100,100,100,100

Javascript: 13kb
CSS: 13kb
Total size: 130kb
Requests: 15
TTFB: 172ms
DOM loaded:     386ms
Loading time: 756ms
Hosted on: CloudFlare (CDN)
Built by: Usecue BV
Score: 99,92,100,100

Javascript: 1kb
CSS: 7kb
Total size: 974kb
Requests: 17
TTFB: 166ms
DOM loaded:     601ms
Loading time: 1s
Hosted at: CloudFlare (CDN)
Built by: Usecue BV
Score: 100,93,100,100

Javascript: 140kb
CSS: 80kb
Total size: 561kb
Requests: 30
TTFB: 52ms
DOM loaded:     528ms
Loading time: 1.05s
Hosted at: unknown
Built by: Delete Agency
Score: 98,100,100,100

The easy steps

First of all you need a low Time To First Byte. All websites in the list above have a TTFB of less than 200ms. This means that the server needs to respond fast. I use CloudFlare for most of my websites, but using a well configured VM works too (as you can see). I am not sure what hosting Delete Agency uses, but they got a nice low TTFB. Getting a low TTFB is mainly a matter of choosing the right hosting. You can test this metric with a tool like Pingdom or GTMetrix. Note that proper (server-side) caching helps a lot too. I use a Static Site Generator to generate my pages, which is essentially the same as using full server-side caching.

Secondly, you need to optimize your images. Use SVG whenever possible and heavily compressed JPG for the rest. If you have to use PNG, make sure you use TinyPNG to compress them and use loading=“lazy” on all image tags. Note that using WebP is not required at all to get a good score. The total page size to aim for is under a 1000kb.

Finally, you need to address all the small issues Google Lighthouse throws at you. These could be accessibility things, but also SEO or performance issues. Note that Performance issues correlate to the speed at which the site loads, not to the checklist, so fixing these issues is optional. A Performance score of 100 represents the 98th percentile.

The blocking code issue

When you have done all the above, you are probably left with some hard to solve ‘blocking code’ issues. Google will suggest to move the Javascript and CSS to the footer, but that does not really solve it. You will get an ugly Flash Of Unstyled Text (FOUT) and your website will only be usable after your code has fully loaded. Here is where I initially got stuck. I found two solutions to fix this blocking issue.

The first approach is perfectly outlined by Delete Agency (the last website in the list). They use a lot of Javascript and CSS, which is typically blocking. Therefore, they had to split and/or inline parts of this code. They documented this process in great detail. The end-result (and the process) is impressive, but it is also an awful lot of work.

Fortunately, there is a much simpler approach. You should simply use less Javascript and CSS and when I say less… I mean significantly less. If you compare the websites built by Usecue BV (that is me) to the website built by Delete Agency you see that I used 10 times less Javascript and CSS. This obviously completely removes the need for inlining and splitting code. When you look at all websites worldwide, the difference between my perfectly scoring websites and the average website is actually more like 20 times less, as the average website contains 400kb Javascript and 60kb CSS. To get these numbers down so drastically I only had to do one thing: stop using (Javascript and CSS) frameworks. Of course this required a learning curve, but I got the hang of it really quickly.

It is a misconception that your total page size should be very very small. You can perfectly load a LOT of large images (as long as you stay under a 1000kb). A homepage twice as big as the one from Delete Agency can still get a perfect score. The problem lies mainly in the blocking Javascript and CSS.

Some closing words

So… an effective strategy for getting a perfect Google Lighthouse score is to stop using Javascript and CSS frameworks. That might seem scary at first, but Javascript and CSS have come a long way. Things like Flexbox, CSS columns and CSS grid handle most of your more complex CSS problems with ease. Cross-browser issues are close to non-existent in the current browser landscape. Stick to writing lean CSS and lean Javascript. It might feel like you are going back to the nineties or the zero’s, but that is okay. Listen to Michael Jackson and sing along. A world without dependencies is a happy place. Heal the world!

A final piece of advice: if you feel insecure about programming Vanilla Javascript, please let Chris Ferdinandy help you. He is an advocate for a simpler World Wide Web and loves to teach. Go make simpler things!

()  Joost van der Schee

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