[webkit-dev] WebKit position on Paint Timing / (first paint, first contentful paint)

Noam Rosenthal noam at webkit.org
Wed Feb 26 11:38:11 PST 2020

On Wed, Feb 26, 2020 at 9:29 PM Maciej Stachowiak <mjs at apple.com> wrote:

> I also suggest to start with "first-paint" as it's perhaps a bit less
> "internal" than FCP, and can provide a performance-regression metric with a
> lesser degree of risk regarding exposing internals / privacy.
> First paint that’s not first meaningful/contentful paint is not a very
> good performance metric IMO. Who cares that a paint happened if it doesn’t
> have any image or text content?
I think it's meaningful as a general regression metric, albeit less useful
than FCP. Web developers are scrambling for any RUM information they can

> I also don’t think this exposes less. The privacy risk here is exposing
> timing data that might be usable for fingerprinting.
Yes, I think that privacy-relevant timing information is already available
through resource timing (window.performance.getEntries("resource")). But
we'll see what the privacy experts come up with.

> What was deprecated was "first meaningful paint" (FMP). FCP was not
> deprecated and has been in wide use for some time.
> What’s the difference between First Meaningful and First Contentful?
FMP had the notion of "primary" content; e.g. it was ignoring
navbars/headers, and trying to figure out when the main content of the site
has been rendered.  As noted, FMP is deprecated. FCP is a lot more
transparent in what it measures.

We will discuss with Apple’s privacy experts what they think of the privacy
> risk. I’m just giving you a rain check for results of this discussion.
Got it, Looking forward :)
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