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An analysis of Chromium's paint timing metrics

Here at SpeedCurve, we are continually gathering detailed performance data from tens of thousands of web pages. This gives us a relatively unique opportunity to analyse and aggregate performance metrics to gain some interesting insights. In this post, I'm going to analyse some browser-based paint timing metrics: First Paint & First Contentful Paint (defined in the Paint Timing spec and implemented in Chromium). I'm also going to analyse First Meaningful Paint (defined in a draft spec and implemented as a Chromium trace metric).

What are paint timing metrics?

The aim of almost any performance optimisation on the web is to improve the user experience. The folk at Google have been pushing this sentiment with a focus on user-centric performance metrics, which aim to answer four questions about users’ experiences:

  1. Is it happening? Is the page that I want to see actually loading?
  2. Is it useful? Has enough content rendered that I can engage with it?
  3. Is it usable? Can I scroll and interact with the page, or is it still loading?
  4. Is it delightful? Are my interactions with the page smooth?

First Paint (FP) measures the point at which pixels are first rendered to the screen after navigating to a new page. First Contentful Paint (FCP) is slightly more specific, in that it measures the point at which text or graphics are first rendered to the screen. Both of these metrics are available in Chromium browsers (Chrome, Opera, Samsung Internet, etc) via the Performance API: performance.getEntriesByType('paint').

The paint timing metrics are important because they aim to answer the first question: is it happening? My analysis will look at performance data from some popular websites in an attempt to figure out whether the paint timing metrics really do answer that question.

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Performance improvement checklist for your whole site

One of the longest-standing items on my performance monitoring tool wishlist is an automatically-generated performance improvement checklist, with the improvements ordered by the impact that they will have on the website. In a previous life, I spent countless hours writing performance reports and conducting A/B performance tests to figure out which change would have the biggest impact on a website's performance.

So I'm understandably very excited that today we're announcing the new Improve dashboard – a prioritised performance improvement checklist that aggregates Lighthouse and Google PageSpeed results across all the URLs in your site to identify the most impactful performance changes you can make.

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Lighthouse scores now available in your test results

In the year since Google rolled out Lighthouse, it's safe to say that "Will you be adding Lighthouse scoring?" is one the most common questions we've fielded here at SpeedCurve HQ. And since Google cranked up the pressure on sites to deliver better mobile performance (or suffer the SEO consequences) earlier this month, we've been getting that question even more often.

We take a rigorous approach to adding new metrics. We think the best solution is always to give you the right data, not just more data. So we're very happy to announce that after much analysis and consideration, we've added Lighthouse scores to SpeedCurve. Here's why – as well as how you can see your scores if you're already a SpeedCurve user.

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Ouch, your JavaScript hurts!

When looking to improve the performance and user experience of our sites we often start by looking at the network:

What's the time to first byte?
How many requests are we making and how long are they taking?
What's blocking the browser from rendering my precious pixels?

While these are entirely valid questions, over the last few years we've seen a growing number of web performance issues that are caused, not by the network, but by the browser's main thread getting clogged up by excessive CPU usage.

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First Input Delay shows how quickly your site responds to user interaction

We're excited to announce the availability of the First Input Delay metric as part of LUX, SpeedCurve's RUM product.

First Input Delay

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Monitor performance budgets at a glance with your Status dashboard

This may sound counter-intuitive, but we don't want you to spend countless hours using SpeedCurve. In fact, our goal is to make your web performance data so accessible, understandable, and actionable that you can get everything you need from us in just a few minutes.

That's why we're so excited to announce the brand-new Status dashboard – a visualization that lets you see at a glance all your web performance budgets, as well as which budgets have been violated.

Keep reading to find out how to start using your Status dashboard to diagnose and fix your performance pains. But first, let's talk about why we built this feature.

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Weekly email reports from your SpeedCurve dashboards

Part of building a strong performance culture in an organisation is lowering the barrier to getting people excited about performance. One of the most effective ways I've found to do this is to send around a performance report every week that can, at a glance, answer an important question: did performance get better or worse?

That was the motivation behind our new Weekly Report feature. Now you can configure any of your Favorites dashboards to be summarized in a weekly email, like this one:

Weekly report email screenshot

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Using RUM to track CPU time

It's exciting working at SpeedCurve and pushing the envelope on performance monitoring to better measure the user's experience. We believe when it comes to web performance it's important to measure what the user sees and experiences when they interact with your site. A big part of our focus on metrics has been around rendering including comparing TTI to FMP, Hero Rendering, and critical blocking resources.

The main bottleneck when it comes to rendering is the browser main thread getting blocked. This is why we launched CPU charts for synthetic testing over a year ago. Back then it wasn't possible to gather CPU information using real user monitoring (RUM), but the Long Tasks API changes that. Starting today, you can track how CPU impacts your users with SpeedCurve's RUM product, LUX.

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Introducing Last Painted Hero

We're excited to announce that we've launched Last Painted Hero as an official metric. Last Painted Hero is a synthetic metric that shows you when the last piece of critical content is painted. Keep reading to learn how Last Painted Hero works, why (and how) we created it, and how it can help you understand how your users perceive the speed of your pages.

The case for smarter heuristics

When choosing the right performance metric, my soapbox for the last few years has been "not every pixel has the same value". In other words, rather than chase dozens of different performance metrics, focus on the metrics that measure what's critical in your page.

Here at SpeedCurve, we think it's good to focus on rendering metrics, because they're a closer approximation to what the user experiences. There are some good rendering metrics out there, like start render and Speed Index, but the downside to these metrics is that they give every pixel the same value. For example, if the background renders and some ads render, that could improve your start render time and Speed Index score, but it might not have a big impact on the user's experience. Instead, it's better to measure the parts of the page that matter the most to users. We call those parts of the page the "hero elements".

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SpeedCurve Consulting Services with Tim Kadlec

We're excited to announce that SpeedCurve is partnering with Tim Kadlec to provide consulting services to our customers!

Tim is a recognized expert when it comes to web performance. He has spoken at numerous conferences including Velocity, Fluent, QCon, SmashingConf, Beyond Tellerand, and WebStock. He wrote High Performance Images and Implementing Responsive Design, as well as contributing to other books. Mark, Tammy and I have each collaborated with Tim on side projects. We're full of gleeful anticipation as we look forward to this opportunity to work together again.

In the first sentence I mentioned that this is a partnership. Here's what that means: Tim will continue to do consulting outside of SpeedCurve, and if you're not a SpeedCurve customer we encourage you to contact him directly. Tim will also be running SpeedCurve's consulting services. This partnership brings special advantages to SpeedCurve customers:

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More RUM metrics in your Favorites dashboards

SpeedCurve comes with a great set of dashboards for synthetic and RUM. But we know that one size does not fit all when it comes to data charts, which is why we've invested so much work into the Favorites dashboards. For customers who use LUX, it provides a place to create custom charts that combine metrics from synthetic and RUM.

We just added some new RUM metrics from LUX in Favorites to allow for even more customized monitoring:

  • Page Views – The number of page views, including Single-Page-App page transitions
  • Sessions – The number of unique sessions
  • Session Length – The number of page views per session
  • Bounced Sessions – The number of sessions that only have one page view
  • Bounce Rate – The percentage of bounced sessions out of the total number of sessions

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Faster test agents and more regions

We’re kicking off 2018 with a bang and a donut. We’ve been busy preparing all-new faster test agents and they’re now available for you to switch to – at no extra cost! 

Go to your Settings to switch to faster test agents.

Faster agents

All our agents now run on much faster AWS C4.Large instances, which better approximate current desktop browsers. We’ve also switched to the latest WebPageTest agent running on Linux.

How much faster? 20-30%

When you switch to the new agents, some of your metrics will get 20-30% faster, so pick a time to switch that suits your team. In between projects or the start of the month are good times to set a new baseline.

Performance Budgets

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How to create a healthy, happy performance culture

One of the best parts of my job is getting to talk to so many people from so many different companies about web performance. Every company is different, and I learn a ton from talking to each one. But one question that almost every person asks me – regardless of what industry they're in or the size of their organization – is this:

How can I create a stronger culture of web performance at my company?

Creating a performance culture means creating a feedback loop in your company or team that looks like this:

Culture Feedback Loop

In other words: Get people to care, show them what they can do to help, and then give them positive reinforcement when you get results. It's basic human psychology, and it might seem obvious when you see it in a super-simple graphic. But it's surprisingly easy to miss these steps and instead skip ahead to the part where you invest in awesome performance tools, and then wonder why all your performance efforts feel like such a painful uphill slog.

In this post, I'm going to share some proven tips and best practices to help you create a healthy, happy, celebratory performance culture. 

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Evaluating rendering metrics

At SpeedCurve, we're fond of the phrase "a joyous user experience". Creating this joy requires delivering what users want as quickly as possible. It's important that the critical content is downloaded and rendered before users get frustrated.

Network metrics have been around for decades, but rendering metrics are newer. Speed Index. Start Render. Time to First Interactive. First Meaningful Paint. These are a few of the rendering metrics that currently exist. What do they mean? How do they compare? Which are best for you? Let's take a look.

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By popular demand: Multiple Favorites dashboards!

Rolling out new features is always a blast, and it's extra rewarding when the new feature is a response to a customer request. We've had many conversations with SpeedCurve users who've told us that multiple Favorite dashboards would be a huge benefit for their teams. 

Favorites Chat

Today, we're very excited to announce that multiple Favorites dashboards are now available. Here's why you need them and how to create them.

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Engagement charts: See correlations between performance and user engagement

One of the best – and worst – things about real user monitoring is that it gives you unparalleled access to massive amounts of user data. The problem is when all this data leads to data indigestion. How do you know where to begin? And how do you know what to leave out in order to present a clear case for performance?

At SpeedCurve, we care about more than just showing you all your data. We want to show you the most important data. And we want to make it easy for you to share that data with people throughout your organization. That’s why we’re excited about the newest addition to our family of visualizations: engagement charts. 

Load Time vs Bounce Rate

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Keeping track of performance changes

Being able to track which changes have an impact – either positive or negative – on your site’s performance is an important part of performance monitoring that can provide valuable feedback to your team. We wanted to make it easier to see at a glance all the changes to your site, without the cognitive overhead of interpreting charts. That’s why we created the new Changes dashboard, which gives you a newsfeed-style overview of recent activity in your SpeedCurve account.

Your Changes dashboard shows your performance budget alerts, deploys, site notes, and SpeedCurve product updates:

Changes dashboard (overview)

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A retailer's guide to web performance

I’m at Shop.org this week, having really interesting conversations with online retailers. What I love about talking with this crowd is that – like me – they're super focused on user-perceived performance. Not surprisingly, we have a lot to talk about.

Making customers happy is the not-so-secret secret to retail success. Delivering a fast, consistent online experience has been proven to measurably increase every metric retailers care about – from conversions and revenue to retention and brand perception. (In fact, there's so much research in this area, I dedicated an entire chapter in my book to it. You can also find a number of great studies on WPO Stats.)

Delivering great, fast online experiences starts with asking two questions:

  • What’s making my pages seem slower for my users?
  • What can I do about it?

The good news is that most of the issues that are making pages slow for your shoppers are right on your pages, which means you have control over them. Here's an overview of the most common performance issues on retail sites, and how you can track them down and fix them. 

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Woohoo! I'm helping build SpeedCurve

I’m super excited to be able to say that I’ve joined Mark, Steve, and Tammy at SpeedCurve!

I’ve watched how Mark has shown over the last couple of years that performance monitoring doesn’t have to be dry and data-heavy; it can be insightful, interactive, and actionable. I’ve also been a follower of Steve’s work for many years. In fact, I should probably thank Steve for providing me with the knowledge that got me interested in web performance in the first place! Tammy’s work has been really interesting to follow, too - her focus on real people and how web performance impacts the way they use our websites is something that resonates strongly with me.

Joseph Wynn

Joseph making BBC News way faster for all users.

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Waterfall with browser events

We've improved our already fantastic interactive waterfall chart with a new collapsed mode that highlights all the key browser events. This lets you quickly scan all the events that happen as the page loads and if you scrub your mouse across the waterfall you can easily correlate each event to what the user could see at that moment.

Along with all the browser metrics you also get to see our new hero rendering times in context. Click on any event to see a large version of that moment in the filmstrip.

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Hero Rendering Times: New metrics for measuring UX

The key to a good user experience is quickly delivering the content your visitors care about the most. This is easy to say, but tricky to do. Every site has unique content and user engagement goals, which is why measuring how fast critical content renders has historically been a challenging task.

That's why we're very excited to introduce Hero Rendering Times, a set of new metrics for measuring the user experience. Hero Times measure when a page's most important content finishes rendering in the browser. These metrics are available right now to SpeedCurve users. 

Hero Rendering Times

More on how Hero Rendering Times work further down in this post. But first, I want to give a bit of back story that explains how we got to here.

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The average web page is 3MB. How much should we care?

A couple of month ago, someone asked if I'd written a page bloat update recently. The answer was no. I've written a lot of posts about page bloat, starting way back in 2012, when the average page hit 1MB. To my mind, the topic had been well covered. We know that the general trend is that pages are getting bigger at a fairly consistent rate of growth. It didn't feel like there was much new territory to cover.

Also: it felt like Ilya Grigorik dropped the mic on the page bloat conversation with this awesome post, where he illustrated why the "average page" is a myth. Among the many things Ilya observed after analyzing HTTP Archive data for desktop sites, when you have outliers that weigh in at 30MB+ and more than 90% of your pages are under 5MB, an "average page size" of 2227KB (back in 2016) doesn't mean much.

The mic dropped. We all stared at it on the floor for a while, then wandered away. And now I want to propose we wander back. Why? Because the average page is now 3MB in size, and this seems like a good time to pause, check our assumptions, and ask ourselves:

Is there any reason to care about page size as a performance metric? And if we don't consider page size a meaningful metric, then what should we care about?

Web performance: page bloat

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Find and fix what matters most

Being able to monitor and measure the performance of your pages is crucial. You know that already. You also know that the next step is to quickly find out what’s hurting your pages so you can stop the pain.

You want to know:

  • Which performance rules is my page breaking?
  • How do I prioritize my optimization efforts?
  • How can I communicate this quickly and clearly to my team?

We’re super excited to announce that you can now use SpeedCurve to answer these questions.

Performance Recommendations

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I've joined SpeedCurve! Here's why

TL;DR

If Mark and Steve invited you to work with them, what would you say? Exactly.

Long version

Okay, I have to elaborate a bit more about why I’m ridiculously excited about working with Mark and Steve. My first foray into the performance space was at the Velocity Conference in 2009. If you had told me then that someday I’d be working with that tall guy rocking the main stage, I would’ve thanked you for the kind words… while secretly thinking you were nuts. But here I am!

Tammy at International Women's Day Tech Talks in Toronto

Tammy at International Women's Day Tech Talks in Toronto

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A/B Testing JSONP and the Preloader with RUM

SpeedCurve is a SPA (Single Page App) so we construct the charts dynamically using JSONP. It works great, but we're always looking for ways to make the dashboards faster. One downside to making requests dynamically is that the browser preloader isn't used. This isn't a factor for later SPA requests, but on the first page view the preloader might still bring some benefits. Or maybe not. We weren't sure, so we ran an A/B test. Long story short, doing the first JSONP request via markup caused charts to render 300 milliseconds faster. 

A/B Test Results

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