The essentials.
- Speed drives conversion: aim for an LCP under 2.5 s on mobile.
- One page, one goal: every page should lead to a clear action.
- Accessibility (WCAG) widens your audience and protects you legally.
- Measure before optimizing: PageSpeed Insights and Search Console are free.
- A lean site uses less energy, loads faster and costs less to host.
The videos.
Chosen for this topic, with our viewing notes.
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8:47EN
Understanding performance with Core Web Vitals
The Chrome team explains the three metrics Google uses to judge a page's experience, and how to read them in its free tools.
Viewing notes
Takeaways
- Three metrics: LCP (loading, under 2.5 s), INP (responsiveness, under 200 ms) and CLS (visual stability, under 0.1).
- Field data (real visitors, the CrUX report) matters more than lab tests.
- PageSpeed Insights and Search Console show these metrics for free, page by page.
Go further
- Web Vitals (opens in a new tab) web.dev (Google) · Documentation
- PageSpeed Insights (opens in a new tab) Google · Tool
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6:43EN
The ultimate guide to web performance
A complete, fast-paced tour of what makes a site fast: images, fonts, scripts, caching. Useful to understand what a good provider should be doing.
Viewing notes
Takeaways
- Measure first (Lighthouse), then fix the heaviest item: almost always images.
- Less JavaScript, loaded later, speeds a page up more than any premium hosting.
- Modern formats (WebP, AVIF), screen-sized images and lazy loading do most of the work.
Go further
- Learn Performance (opens in a new tab) web.dev (Google) · Course
- Lighthouse overview (opens in a new tab) Chrome for Developers · Documentation
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2:39FR
L'accessibilité numérique à toutes les étapes d'un projet
Atalan, a French accessibility agency, shows in under three minutes why accessibility is decided at the scoping stage, not at the end of the project.
Viewing notes
Takeaways
- Accessibility spans design, content and code: every role has a part.
- Planned from the start it costs little; retrofitted, it costs a lot.
- RGAA (France) and WCAG (international) are the standards to require in a brief.
Go further
- RGAA, accessibilité numérique (opens in a new tab) État français · Official text
- WCAG overview (opens in a new tab) W3C WAI · Official text
Videos are hosted by YouTube. Nothing is loaded from Google until you press play; the player then uses youtube-nocookie.com, YouTube's privacy-enhanced mode.
Test yourself.
A few minutes to check what you remember from this topic.
This topic is part of the paths : Launch or redesign my website.
The resources.
- Learn Performance
Google's reference course on web performance.
Open (opens in a new tab) ↗ - Web Vitals
LCP, INP, CLS: the experience metrics Google uses.
Open (opens in a new tab) ↗ - Milliseconds Make Millions
The study that measures the effect of 0.1 s on conversions.
Open (opens in a new tab) ↗ - PageSpeed Insights
Measure the real-world speed of any page.
Open (opens in a new tab) ↗ - Lighthouse overview
Chrome's built-in audit tool: performance, accessibility, SEO.
Open (opens in a new tab) ↗ - MDN Learn web development
HTML, CSS and JavaScript fundamentals, by Mozilla.
Open (opens in a new tab) ↗ - WCAG overview
The international web content accessibility guidelines.
Open (opens in a new tab) ↗ - RGAA, accessibilité numérique
France's accessibility framework and its criteria.
Open (opens in a new tab) ↗ - 10 Usability Heuristics
The ten most-cited usability principles in the world.
Open (opens in a new tab) ↗ - Laws of UX
Psychology laws applied to interface design.
Open (opens in a new tab) ↗ - E-commerce UX research
The largest research base on e-commerce usability.
Open (opens in a new tab) ↗ - Référentiel général d'écoconception (RGESN)
France's official eco-design practices for digital services.
Open (opens in a new tab) ↗ - Website Carbon Calculator
Estimate the carbon footprint of a web page.
Open (opens in a new tab) ↗ - Baromètre France Num 2025
Digital and AI in French small businesses, official figures.
Open (opens in a new tab) ↗
Websites
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