Have you ever started reading an exciting news article but then lose your line because all the text shifted downwards? This happens to me a lot, mostly because of ads loading around the content I’m reading.
This kind of user experience can be frustrating, but until now we’ve had trouble measuring it quantitatively. Cumulative Layout Shift addresses this challenge.

Embedding an existing library or service as a third party can increase productivity, but often has a cost on perceived performance. Once you embed external code, how can you ensure that this code will not affect the performance and interactivity of your site? Here are some ideas for a more efficient third party code.

Loading a web page requires fetching a whole set of resources which collectively allow the page to be displayed and interacted with. To increase the user’s perception of speed, you may need to influence the order in which these resources are fetched and executed. And that’s where preload and Resource Hints come in.

How to properly measure how fast a web page starts to display its content? Several Web performance metrics exist to answer this question, including First Paint, Start Render and one of the newest: First Contentful Paint (FCP). How does FCP stand out, what are its limitations? Let’s dive into the metrics that measure the browser’s early rendering of web pages.

When we talk about web performance measurement, what we’re actually trying to determine is the moment when a user can effectively achieve his or her goal. Meaning the users can consult the content they are looking for and/or interact with the page  in a satisfactory way. Some metrics endorse rendering actions by the browser, others measure the progress of the display through the recording of a video. However, a great mystery remains: how to properly measure interactivity.

For a few years now, Google has been pushing an ambiguous metric: Time To Interactive. What does it mean? Let’s define it and explain how and when to use it (or not).

Images are a key content on your website? If you’re serious about your website performance, you have probably optimized them. But have you considered to lazy load your images? Lazy loading images improves the user experience by saving bandwidth for important content first.

Some reject the technique for SEO considerations. But properly lazy loading your images does not prevent them from being indexed. Let’s find out why you should implement lazy load, and how to make sure you build it in a SEO friendly way.

Cookies are widely used throughout the Web because they allow publishers to store data directly on the user’s Web browser. They’re particularly used to identify the user’s session, allowing the web server to recognize the user as they navigate through the site, and generally contain sensitive data. You have to properly protect them.
Continue reading Secure your Cookies (Secure and HttpOnly flags) →

Improving the speed at which a web page is displayed often means making the browser’s life as easy as possible. When the browser receives an HTTP response, it actually receives text encoded in bytes, where each byte or sequence of bytes represents a given character. If the browser does not have a clear information about the used encoding, it will waste time trying to guess and may fail in some cases.

Continue reading Content Encoding: why and how to use the meta charset tag and the Content-Type header →

This article is a transcript of my conference about Performance Budgets, held during the We Love Speed event (Bordeaux, October 9, 2018). Continue reading Performance Budgets – We Love Speed 2018 →

Using a tag manager does come with consequences on your web pages loading speed. In a previous post, we’ve pointed out that this impact can’t be limited to the asynchronous loading of the embedded tags, and that your tag manager can become a serious problem for your website performance. So now it’s time to explore a few best practices about tag management so that this tool could meet its marketing goals without compromising your webpages’ speed. With the help of L’Oréal’s Digital Ad Tech Manager and several experts. Continue reading Tag Manager & Web Performance Part 2: a question of discipline and collaboration →