Introduction to UX Speed

In this short workshop, Sergey Chernyshev will discuss why the Speed of User Experience matters and how to determine if your site is fast or slow.

He will talk about web performance metrics in general and introduce Core Web Vitals - a set of metrics most commonly used to measure UX Speed.

Sergey will then show a few most common problems causing slowdowns, and how to fix them. Don’t miss out on making your web experience speedier and better!

Transcript

1. Sergey Chernyshev — May 19, 2026 Introduction to UX Speed FKA Web Performance NY UX Speed & Web Performance Meetup
2. Speed Engineer Designer • Web Performance engineer • Cloud fl are • Open Source developer • Organizer of NY UX Speed
 & Web Performance Meetup • Google Developer Expert
 in Web Performance • RUM-CG Member Sergey Chernyshev
3. Awesome Website!
5. Sloooowly
6. Even Slower
8. S TAT S • Relive: 50% faster LCP & ~0 CLS across => +3% conversion, -6% bounce (2025) • Adobe: LCP 7.2 to 3.4 seconds => +35% visits, +21% time on mobile (2023) • Pinterest: -40% wait time => +15% SEO, +15% conversion (2017) • Trainline: -300ms latency => +$11.5M / year revenue (2016) • Etsy: +160Kb => +12% bounce rate (2014) • Edmunds: -77% load time => +20% page views (2011) • Mozilla: -2.2s => +15.4% Downloads (2010) • Google: +400ms => -0.21% searches after experiment! (2009) • Amazon: +100ms => -1% revenue (2008) • Google: +500ms => -25% searches (2006) WPOStats.com
9. W H Y D O W E M E A S U R E S P E E D ? • Monitor for degradations (Ops) • Analyze code for perf issues (Devs) • Verify improvements (Devs, QA) • Prioritize improvements (Business) • Budget for WPO initiatives (Business)
10. S Y N T H E T I C T E S T I N G & A N A LY S I S • From particular location • Tester controls instrumentation • One metric value • Data can have lots of details for analysis
11. R E A L U S E R M E A S U R E M E N T • Real users (a lot of them) • A lot of data (need to store it) • All noise you can get, requires filtering • Metrics are distributions • Can correlate to business KPIs
12. M E T R I C S E V O L U T I O N • DNS, SSL/TLS, Time To First Byte (TTFB) • Page Load, Document Complete, Fully Loaded • First Paint, Above the Fold Time (AFT), SpeedIndex • First Contentful Paint (FCP) • Core Web Vitals
13. Core Web Vitals
14. Largest Contentful Paint Loading of User Experience
15. Interaction to Next Paint Interactivity of User Experience
16. Cumulative Layout Shift Visual Stability of User Experience
17. M E T R I C S E V O L U T I O N • DNS, SSL/TLS, Time To First Byte (TTFB) • Page Load, Document Complete, Fully Loaded • First Paint, Above the Fold Time (AFT), SpeedIndex • First Contentful Paint (FCP) • Core Web Vitals • What are metrics for your product?
21. DESIGN FOR SPEED with progressive enhancement
22. MOVIES OR PAINTINGS? Speed vs. Fluency, What drives user engagement? Kent Alstad, Velocity NY 2015
23. PERFORMANCE CHOREOGRAPHERS Performance Choreography Tim Kadlec, WebPerfDays NY 2014
24. PROGRESSIVE ENHANCEMENT ➤ Main goals: 1. Enable features based on browser capabilities (e.g. JavaScript, image formats, local storage, gyro/compass) 2. Reveal features as page is being downloaded and constructed (render basic html + CSS, add JS handlers, fonts, etc)
25. FEATURES BASED ON CAPABILITIES book by Filament Group fi lamentgroup.com/dwpe/
27. Q&A https://uxspeed.dev/