There's been an explosion in 3rd-Party Tags…

And as Tim Kadlec once said "Everything should have a value, because everything has a cost".

So how do we measure the performance cost of all the 3rd-party tags we keep adding to our sites?

If you’ve got your own Private WebPageTest instance, and you want to add extra locations without setting up the test agents yourself then you can add agents from another instance.

Once configured your local WebPageTest instance submits tests and retrieves results via the API of the remote WebPageTest instance (aka Relay Server), and the pages are tested on the remote instance’s agents.

Using a Relay Server is also handy if you want to do local development on the server code without needing to setup Windows (or mobile) test agents.

So Google, a group of publishers and others have launched Accelerated Mobile Pages (AMP)

AMP promotes the goal of a faster mobile web which is something I think we’d all like to see.

If you visit g.co/ampdemo on a mobile, and search for ‘Obama’ there’s no doubt the stories in the carousel come up fast, and moving between them is slick too. The demo isn’t available in all regions yet so Addy Osmani posted a demo to YouTube.

Similar to Google’s Instant Pages, AMP relies on pre-rendering and caching to make the pages load instantly.

The pre-loader (also known as the speculative or look-ahead pre-parser) may be the single biggest improvement ever made to browser performance.

During their implementation Mozilla reported a 19% improvement in load times, and in a test against the Alexa top 2,000 sites Google found around a 20% improvement.

It’s not a new browser feature but some seem to believe it’s Chrome only and yet others suggest it’s “the most destructive ‘performance enhancement’ there’s ever been”!

So what is the pre-loader and how does it improve performance?

With our current tools it’s relatively easy to examine the performance of a single page, or the performance of a journey a visitor takes through a series of pages but when I examine a client’s site for the first time I often want to get a broad view of performance across the whole site.

There are a few tools that can crawl a site and produce performance reports, SiteSpeed.io from Peter Hedenskog and NCC Group’s (was Site Confidence) Performance Analyser are two I use regularly.

Sometimes I want more than these tools offer - I might want to test from the USA or Japan, or want some measurements they don’t provide - that’s when I use my own instance of the HTTP Archive.