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2020 Chrome Dev Summit: Web Performance 101

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What do we mean when we talk about "web performance"? Why should you care about it? How can measure it? How do you get other people in your organization to care? In this workshop at the 2020 Chrome Dev Summit, I covered these questions – including an overview of the history of performance metrics, up to Core Web Vitals.

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2020 Chrome Dev Summit: Web Performance 101

  1. 1. Web Performance 101: What is web performance and why should I care? @tameverts #ChromeDevSummit ¯_(ツ)_/¯
  2. 2. @tameverts
  3. 3. speedcurve.com/benchmarks/
  4. 4. What is “web performance”? Why should I care about it? How do I measure it? How can I get other people in my company to care about it?
  5. 5. Slow websites suck.
  6. 6. the average web user believes they waste two days a year waiting for pages to load
  7. 7. “web stress” When apps or sites are slow, we have to concentrate up to 50% harder to stay on task. @tameverts
  8. 8. 11 When do users start to interact with a page?
  9. 9. 12 Source: Jakob Nielsen
  10. 10. 13 Source: Jakob Nielsen
  11. 11. 14
  12. 12. 15 “We want you to be able to flick from one page to another as quickly as you can flick a page on a book. So, we’re really aiming very, very high here… at something like 100 milliseconds.” Urs Hölzle SVP Engineering, Google
  13. 13. fast slow @tameverts
  14. 14. Slow pages affect people’s perception of three things completely unrelated to time: 1. Content “boring” 2. Visual design “tacky” “confusing” 3. Ease of navigation “frustrating” “hard-to-navigate”
  15. 15. User experience and web performance are predictable indicators of business outcomes.
  16. 16. Rebuilding Pinterest pages for performance resulted in 40% decrease in wait time, 15% increase in SEO traffic, and 15% increase in signup conversion rate. Ancestry.com saw a 7% increase in conversions after improving render time by 68%, page weight by 46% and load time by 64%. Staples reduced median page load time by 1 second and 98th percentile load time by 6 seconds, resulting in a 10% conversion rate increase. @tameverts
  17. 17. @tameverts
  18. 18. @tameverts
  19. 19. optimal load times for peak conversions @tameverts
  20. 20. even 100ms delays matter @tameverts
  21. 21. real user data + machine learning
  22. 22. collected 1M+ beacons of real user data across 93 attributes, including… • top-level – domain, timestamp, SSL • session – start time, length (in pages), total load time • user agent – browser, OS, mobile ISP • geo – country, city, organization, ISP, network speed • bandwidth • timers – base, custom, user-defined • custom metrics • HTTP headers
  23. 23. sessions that convert have fewer images
  24. 24. @tameverts
  25. 25. pages with more scripts are less likely to convert
  26. 26. 160+ scripts… uh-oh @tameverts
  27. 27. speakerdeck.com/csswizardry/its-my-third-party-and-ill-cry-if-i-want-to
  28. 28. How fast is fast enough?
  29. 29. “The real thing we are after is to create a user experience that people love and they feel is fast… and so we might be front-end engineers, we might be dev, we might be ops, but what we really are is perception brokers.” Steve Souders
  30. 30. But measuring perception is hard. It’s even harder to scale.
  31. 31. What tools do we use? Synthetic (lab) Consistent baseline Mimics network & browser conditions No installation Compare any sites Detailed analysis Waterfall charts Filmstrips and videos Limited URLs Real user monitoring (field) Requires JavaScript installation Large sample size (up to 100%) Real network & browser conditions Geographic spread Correlation with other metrics (bounce rate) No detailed analysis Only measure your own site
  32. 32. @tameverts
  33. 33. @tameverts
  34. 34. @tameverts
  35. 35. Free tools to explore Synthetic webpagetest.org developers.google.com/speed/ pagespeed/insights/ Real user monitoring github.com/bluesmoon/boomerang developers.google.com/web/tools/ chrome-user-experience-report
  36. 36. webpagetest.org
  37. 37. developers.google.com/speed/pagespeed/insights/
  38. 38. A brief history of performance metrics
  40. 40. ❑ Correlates to what users actually see in the browser ❑ Is easy to use and accessible right out of the box ❑ Recognizes that not all pixels and page elements are equal ❑ Allows us to customize what we measure on specific pages The best UX metric…
  41. 41. Is it happening? Is it useful? Is it usable? Is it delightful? developers.google.com/web/fundamentals/ performance/user-centric-performance-metrics
  42. 42. Load Time The time from the start of the initial navigation until the beginning of the window load event
  43. 43. Start Render The time from the start of the initial navigation until the first non-white content is painted
  44. 44. start render repeat visits
  45. 45. wow!
  46. 46. First Paint First Contentful Paint First Meaningful Paint
  47. 47. First Paint (FP) Pixels first start to render
  48. 48. First Contentful Paint (FCP) Text and graphics start to render… BUT often catches non-meaningful paints (e.g. headers, nav bars)
  49. 49. First Meaningful Paint (FMP) The paint after which the biggest ATF layout change has happened and web fonts have loaded
  50. 50. speedcurve.com/blog/an-analysis-of-chromiums-paint-timing-metrics/
  51. 51. Analysis of 40 top Alexa-ranked sites 95% of FP events occur before Start Render 85% of FCP events occur before Start Render 50% of FMP events occur before Start Render speedcurve.com/blog/an-analysis-of-chromiums-paint-timing-metrics/
  52. 52. Speed Index Average time at which visible parts of the page are in the viewport
  53. 53. ❑ Correlates to what users actually see in the browser ❑ Is easy to use and accessible right out of the box ❑ Recognizes that not all pixels and page elements are equal ❑ Allows us to customize what we measure on specific pages The best UX metric…
  54. 54. Custom metrics Measure performance with high-precision timestamps Available in both synthetic and RUM (yay!) https://www.w3.org/TR/user-timing/ https://speedcurve.com/blog/user-timing-and-custom-metrics/
  55. 55. how long does it take to display the main product image on my site?
  56. 56. Time to First Tweet The time from clicking the link to viewing the first tweet on each page’s timeline Pinner Wait Time (PWT) The time from initiating an action (e.g., tapping a pin) until the action is complete (pin close-up view is loaded) Time to Interact (TTI) @tameverts
  57. 57. Lighthouse Scores based on audits run on synthetic tests. Checks your page against “rules” for Performance, PWA, Best Practices, and SEO. For each category, you get a score out of 100 and recommendations for what to fix. developers.google.com/web/tools/lighthouse
  58. 58. matuzo.at/blog/building-the-most-inaccessible-site-possible- with-a-perfect-lighthouse-score/
  59. 59. Core Web Vitals
  60. 60. developers.google.com/search/blog/2020/11/timing-for-page-experience
  61. 61. “Core Web Vitals are the subset of Web Vitals that apply to all web pages, should be measured by all site owners, and will be surfaced across all Google tools. “Each of the Core Web Vitals represents a distinct facet of the user experience, is measurable in the field, and reflects the real-world experience of a critical user-centric outcome. “The metrics that make up Core Web Vitals will evolve over time. “The current set for 2020 focuses on three aspects of the user experience — loading, interactivity, and visual stability — and includes the following metrics… web.dev/vitals/
  62. 62. Largest Contentful Paint First Input Delay Cumulative Layout Shift loading interactivity visual stability
  63. 63. 75th percentile of page loads across mobile and desktop
  64. 64. Amount of time it takes for the largest visual element to render. Available in Chrome and Chromium-based browsers. Measurable via synthetic and RUM.
  65. 65. Amount of time it takes for page to respond to user input (e.g. click, tap, key). Only measurable via RUM.
  66. 66. FID can seem fast because user interactions take place later in the page’s rendering cycle... after CPU-hogging long tasks have completed. speedcurve.com/blog/first-input-delay-google-core-web-vitals/
  67. 67. No correlation when looking at all sessions speedcurve.com/blog/first-input-delay-google-core-web-vitals/
  68. 68. Stronger correlation at 75th percentile speedcurve.com/blog/first-input-delay-google-core-web-vitals/
  69. 69. Long Tasks have a high correlation across the board speedcurve.com/blog/first-input-delay-google-core-web-vitals/
  70. 70. Long Tasks Measures JavaScript functions that take 50ms or longer. Long or excessive JS tasks can delay rendering, as well as cause page “jank”. Measurable via synthetic and RUM.
  71. 71. Score that reflects how much page elements shift during rendering. Available in Chrome and Chromium-based browsers. Measurable via synthetic and RUM.
  72. 72. Size of the shifting element matters speedcurve.com/blog/visualising-cls-layout-shifts/
  73. 73. Image carousels can generate false positives speedcurve.com/blog/visualising-cls-layout-shifts/
  74. 74. Web fonts & opacity changes can cause issues speedcurve.com/blog/visualising-cls-layout-shifts/
  75. 75. Bounce rate gets worse as CLS degrades Bounce rate improves as CLS degrades Bounce rate stays the same as CLS degrades @tameverts
  76. 76. Look at your own data.
  77. 77. How do these metrics correlate with my business goals? How fast should they be? How do we stay on track?
  78. 78. cnet.com/news/appliance-science-the-well-done-physics-chemistry-of-the-toaster/
  79. 79. How to create a culture of performance
  80. 80. “The largest hurdle to creating and maintaining stellar site performance is the culture of your organization. Lara Hogan designingforperformance.com
  81. 81. “No matter the size or type of team, it can be a challenge to educate, incentivize, and empower those around you. “Performance more often comes down to a cultural challenge, rather than simply a technical one.” Lara Hogan designingforperformance.com
  82. 82. Educate Incentivize Empower
  83. 83. 2009 Improved average load time from 6s  1.2s 7-12% increase in conversion rate + 25% increase in PVs Average load time degraded to 5s User feedback: “I will not come back to this site again.” Re-focused on performance 0.4% increase in conversion rate 2010 2011 @tameverts
  84. 84. 1. No front-end measurement 2. Constant feature development 3. Badly implemented third-parties 4. Waiting too long to tackle performance problems 5. Relying on performance sprints
  85. 85. 1. You need a plan
  86. 86. Making it up as you go is not always a good idea. (Actual photo taken yesterday of my family’s gingerbread village.)
  87. 87. Tools ≠Enough
  88. 88. 2. Have a champion higher up
  89. 89. 3. Then build a cross-disciplinary team
  90. 90. Everyone who touches a page should care about the performance of that page.
  91. 91. Embrace performance from the ground up. Embed engineers into other teams. Enlist performance ambassadors. Teach people how to use (or at least understand) the monitoring tools you use.
  92. 92. 4. Set shared goals
  93. 93. It’s perilously easy to accidentally become a gatekeeper.
  94. 94. We first went to the engineering leaders, and then we went to our product leader. Our pitch was totally different... Reefath Rajali // PayPal chasingwaterfalls.io/episodes/episode-two-with-reefath-rajali/
  95. 95. “When we went to our product leaders, we spoke more about the business numbers and the business benefits. “When we spoke to our engineering leaders, it was more about our consumer delight.” Reefath Rajali // PayPal chasingwaterfalls.io/episodes/episode-two-with-reefath-rajali/
  96. 96. Find out what people care about
  97. 97. ❑ bounce rate ❑ cart size ❑ conversions ❑ revenue ❑ time on site ❑ page views ❑ SEO ❑ user happiness ❑ user retention ❑ competitors
  98. 98. If they care about business metrics…
  99. 99. If they care about user engagement…
  100. 100. If they care about SEO…
  101. 101. If they care about third parties…
  102. 102. Who they are What they care about What to show them Executives Competition Business impact Benchmarks (filmstrips and videos) Correlation charts (perf + KPIs) Marketing Third parties Traffic + engagement SEO Content Third-party performance Correlation charts (perf + bounce rate) Lighthouse SEO audits Image size Devs / engineers Well, lots of stuff, probably Consult with perf team
  103. 103. 5. Make everyone accountable
  104. 104. Performance budgets FTW!
  105. 105. Thresholds YOU create for metrics that are meaningful for YOUR site addyosmani.com/blog/performance-budgets/ Milestone timings (e.g. start render) Quantity-based (e.g. image weight) Rules-based (e.g. Lighthouse scores)
  106. 106. A good performance budget should show you… What your budget is When you go out of bounds How long you’re out of bounds When you’re back within budget
  107. 107. zillow.com/tech/bigger-faster-more-engaging-budget/
  108. 108. zillow.com/tech/bigger-faster-more-engaging-budget/
  109. 109. Super important! Look at your own data Monitor your competitors No sandbagging allowed Take a step-by-step approach if necessary Use synthetic and RUM (numbers may will vary)
  110. 110. Pro tips Create budgets for your popular and regularly changing pages Review violations early and always Compare before and after releases Update budgets accordingly zillow.com/engineering/bigger-faster-more-engaging-budget/
  111. 111. Who What Metric Ops Back-end issues TTFB Marketing Most important content Third parties SEO Largest Contentful Paint JS Long Tasks Lighthouse SEO score & audits Devs / engineers How well pages are built Performance issues Start Render, Web Vitals Lighthouse Performance audits
  112. 112. Give people ownership
  113. 113. “One of the original directives of the performance team was we weren’t going to set ourselves up to be performance cops.” Dan Chilton, Vox Media responsivewebdesign.com/podcast/vox-media-performance/
  114. 114. “We weren’t going to go around slapping people on the wrist, saying, ‘You built an article that broke the page size budget! You have to take that down or change that immediately!’ “Our goal setting out was to set up best practices, make recommendations, and be a resource within the company that people can turn to when they have to make performance-related decisions.” Dan Chilton, Vox Media responsivewebdesign.com/podcast/vox-media-performance/
  115. 115. 6. Communicate
  116. 116. “We, as engineers, should learn how to show the impact on anything we do.” Malek Hakim // Priceline chasingwaterfalls.io/episodes/episode-one-with-malek-hakim/
  117. 117. How often is often enough? Wall monitors and dashboards 24/7 Alerts (to people who can make fixes) in realtime Reports no more than 1X week Meetups, hackathons, etc. monthly (if possible)
  118. 118. 7. Don’t forget to celebrate!
  119. 119. !!!
  120. 120. medium.com/the-telegraph-engineering
  121. 121. Score some easy wins
  122. 122. “The dull boring stuff” ~Andy Davies Scripts (especially third parties) Images Extraneous code Defer assets where possible
  123. 123. Shaved 15KB off logo Ran A/B test Increased bookings chasingwaterfalls.io/episodes/episode-one-with-malek-hakim/
  124. 124. In summary…
  125. 125. There’s no magic. Show up with a plan. Do the work. (Be patient.)
  126. 126. Thanks! @tameverts speedcurve.com/blog