Core Web Vitals on iOS

Safari’s getting Core Web Vitals in 2025. Are you ready?

Get Prepared

When Google announced Core Web Vitals were coming to Chrome in 2020, the web performance industry was a frenzy! Everyone wanted to get their sites in shape, and it was a great time for web performance.

Five years on, Core Web Vitals have worked! The web as an ecosystem has gotten steadily faster across the board:

Or has it?

Get Ahead of the Curve

Core Web Vitals on (Mobile) Safari

It’s important to view Core Web Vitals through two distinct lenses:

1. Core Web Vitals, the metrics: Largest Contentful Paint, Interaction to Next Paint, and Cumulative Layout Shift. These metrics are platform agnostic and defined in a spec that any other browser is free to implement. Firefox already has!
2. The Chrome User eXperience Report (CrUX): The public dataset used by Google as a ranking signal for SEO. This is specific only to Chrome, so any other browser—including Chrome on iOS!—is a blind spot.

These two points yield two corresponding problems…

1. Apple haven’t implemented any of the Core Web Vitals in their own browser, Safari, and;
2. Apple, until iOS 17.4, hasn’t allowed any non-WebKit browser engine on the iOS platform.

This means that we’ve had zero visibility of the Core Web Vitals metrics on iOS or any flavour of Safari at all. If you’re based in North America or northwestern Europe, that may mean the majority of your audience is completely unaccounted for.

However, things are about to change.

Beat the Competition

Core Web Vitals Come to Safari

Apple announced that Largest Contentful Paint and Interaction to Next Paint will be coming to Safari as part of the Interop 2025 project! This means that we can begin tracking and instrumenting two of the three Core Web Vitals before the end of the year!

Are You Prepared?

If you’ve been focusing on Core Web Vitals for your Chrome visitors already, you’re well poised. But are you prepared for what it might mean for the business? Are your developers prepared for the different rendering engine? Do you know how to track site-speed in Safari if the data doesn’t go into CrUX?

Get the Workshop

To help prepare clients—both new and old—I’ve designed a one-day workshop covering, but not limited to:

• Apple, Safari, and Core Web Vitals
  • Why can’t we get Core Web Vitals on iPhones?
  • Why can’t we get Core Web Vitals in Safari?
  • What even is Chrome on iOS?
• Key events
  • LCP is coming to Safari in 2025!
  • Blink can run on iOS as of 17.4 (but it still doesn’t)
• What does Safari mean to you?
  • Based on your own audience, how much does it matter to you?
  • Can we infer anything from existing Core Web Vitals data?
• How does Safari differ from Chrome?
  • WebKit vs. Blink
  • JavaScriptCore vs. V8
  • Performance API availability
  • Interop 2025
• Do the same optimisation techniques apply?
  • Can we reuse the same work we did for Chrome?
  • Do we need to do anything differently?
  • Does Safari need special treatment?
• How do we measure Safari in the wild?
  • If it’s not in CrUX, where is it?
  • Real user monitoring
  • Which metrics can we capture
• Safari on localhost
  • Safari-specific devtools
  • Tips, tricks, and workflows
  • Testing real devices

Harry gave the team a strong footing for identifying performance issues on iPlayer. With his knowledge, we were able to roll out quick fixes to our audiences without the need for big rewrites, all within just two days.

— Matthew Burrows, BBC iPlayer

The goal is to leave the team aware of the upcoming changes, arm them with tools and knowledge to optimise for the different engines, and ensure that your Safari users aren’t being overlooked.

Remote or In-Person

I much, much prefer in person workshops—it means we can hang out and probably head for drinks after! But as it’s only a single day, running the workshop remotely works pretty naturally. Remote workshops will be recorded for you to keep.

Ready? Let’s get it booked in!

Arrange the Workshop