Performance regression testing
Changes reach your users from everywhere: your own teams, third parties, the browser, the OS. Each one is small. Together they're death by a thousand cuts, and in most organisations nobody owns the whole journey.
I've always considered myself a QA engineer, not a performance specialist, but just over a year ago I set out to find ways to warn us about performance regressions before release. This talk is about what I've learned from the web performance community, what I built when off-the-shelf tools didn't fit, what I found, and where the numbers lied to me. That last part includes CI noise, unrealistic throttling, and why "LCP doubled" isn't always bad news.
You'll leave with a tester's view of web performance, some ideas for turning an existing test suite into a regression detector, and a few home-made acronyms.
Risko Ruus
Risko is a Principal QA Engineer at Rush Street Interactive with over 20 years of experience in software quality, development, and test automation. His background includes work on the Nokia smartphone OS, Skype, and mobile betting apps.
He focuses on helping teams deliver software quality beyond functional correctness, including non-functional requirements such as performance, reliability, and user experience. Recently, he has been building a testing library that brings visual assertions into UI tests using images, videos, and vision-capable LLMs.
Outside work, he enjoys backcountry hiking and learning Japanese.
Long-term performance
When it comes to web performance, it pays to think in milliseconds. But it’s also worth stepping back and looking at longer timescales. In this talk, we’ll look at a website that’s been online for decades.
We’ll take a look at what technologies and techniques have emerged and disappeared over the years. What worked, what didn’t, what made the most difference, and what has stood the test of time.
Making a fast website can be challenging enough; keeping a website fast is harder still!
Jeremy Keith
Jeremy lives in Brighton, England where he makes websites with the splendid design transformation consultancy Clearleft. You may know him from such books as HTML5 For Web Designers and Resilient Web Design. He’s also the curator of the Web Day Out and UX London conferences.
When he’s not playing traditional Irish music on the mandolin, Jeremy spends most of his time goofing off on the internet, documenting his time-wasting on adactio.com, where he has been writing for over twenty years.
Core Mobile Vitals: Building the Missing Standard for Apps
Mobile has no Core Web Vitals. It has crash rates and ANRs, and neither tells you whether the app felt good to use.
This isn't the first attempt to fix that. Previous attempts came from individual vendors, stopped at a dashboard, and never connected to revenue or told a developer what to actually change. None of them became a shared language, and it's fair to be skeptical of the next one.
Core Mobile Vitals is being built differently: as an open standard rather than a product, validated against real user data, and scoped so a score ties to business impact on one end and a specific fix on the other. It started by borrowing from the web, then discovering how much doesn't transfer. LCP assumes a page load. CLS assumes a document. Neither survives a persistent app process. This talk covers what we kept, what we threw out, and the four pillars we landed on: screen load, smoothness, responsiveness, and stability. You'll get the first public look at the metrics, plus an honest account of what it takes to make a standard that sticks.
Cliff Crocker
Cliff Crocker has been working in web performance for longer than he'd probably like to admit. He currently leads product for Front-End Observability at Palo Alto Networks, bringing together web and mobile observability following the acquisitions of SpeedCurve and Embrace.
Over the years, Cliff has approached performance from just about every angle, as a practitioner at Walmart, building performance products at SOASTA and Akamai, helping teams make sense of the web at SpeedCurve, and more recently diving deep into mobile observability at Embrace. Through it all, he's remained focused on the same question: how do we better understand what our users are actually experiencing?
These days, that question increasingly spans web, mobile, and everything happening in between.
Jason Pamental: MC
Jason is a Principal Designer at Chewy.com, helping lead their design system efforts across ecommerce, enterprise, and mobile app experiences.
Previously, he spent much of his time working with clients to establish their typographic systems and digital strategy, helping design and development teams works smarter and faster, and running workshops about all of the above. He is a seasoned design and user experience strategy leader with over 20 years’ experience on the web in both creative and technical roles. Past clients range from state governments, type industry giants, Ivy League and High Tech, to the NFL and America’s Cup.
Jason researches and writes extensively on typography for the web. He’s author of Responsive Typography from O’Reilly, pens articles for .Net Magazine, PRINT Magazine, HOW, Monotype.com, frequently joins as a guest on podcasts, and has authored online courses for Aquent’s Gymnasium platform and Front-end Masters. Jason’s an experienced speaker and workshop leader, having presented at over 100 national and international conferences.
The real story: mainly he just follows Leo and Henry around Turner Reservoir, posting photos on Instagram.
Robin Marx: MC
Dr. Robin Marx is a Web Performance Expert at Akamai Technologies. He focuses on the performance and workings of modern Web protocols like HTTP/2, HTTP/3 and QUIC and has been a contributor in the IETF QUIC working group for multiple years.
Robin often talks about web performance at international conferences, making the complex situations more insightful to the wider public. On the weekends, he likes to hit other people with longswords.
Latest on Web Compression
With 2 years of rollouts, we've learned a lot about compression dictionaries and the Web. Patrick will cover what works, where the footguns are, how to maximize their effectiveness, and about other experiments conducted during that time around compressing content on the web.
Pat Meenan
Patrick Meenan has spent over 25 years working on web performance at companies like Google, Facebook, Cloudflare, and AOL. Best known as the creator of WebPageTest, he is an active contributor to web standards and is currently an engineer on the Chrome team, working to make the web faster.
Standards from the Field
Web developers are constantly pushing the boundaries of the web’s standard capabilities, and that’s by design: our languages are meant to be composed and extended to build websites that do exactly what we need. Sometimes though, our custom solutions highlight deeper challenges with performance and usability that limit us all, and reveal an opportunity for the web’s native capabilities to grow. How do we know when we’ve stumbled upon a common solution, and what does it really look like to move from patterns that work on one website to features that are built into our browsers—particularly if that sort of work is not your main gig?
In this talk, Scott will share examples of how he and his teammates not only build with web standards, but sometimes help propose, specify, and build those standards themselves. Along the way, he’ll highlight upcoming and newly shipped features that you can use today to deliver faster, more accessible websites, and illuminate the process of how those features came to be.
Scott Jehl
For over two decades, Scott has worked at the intersection of design and front-end technology, leading projects for some of the Web’s most iconic brands. Scott is best known for his work within the web community, advocating for practices and building tools that enable websites to reach the broadest possible audience, and contributing to the specs and implementation of several web standards.
These days, he is an engineer at Squarespace in New York City, where his team oversees the performance and accessibility of millions of websites.
Scott is the creator of the Web Components Demystified online course (2024), author of Responsible Responsive Design (2014, A Book Apart), and co-author of Designing with Progressive Enhancement (2010, New Riders).
Performance as a Design Opportunity
Every “perfectly loaded” mockup is a lie developers will have to fix. Performance usually lands on developers after design is signed off, leaving them to improvise loaders, errors, way too much data, and more. Meanwhile, designers see performance as a constraint, or as a checklist item: “don’t forget the spinner.” What if we saw it as a design opportunity instead?
Based on real-life projects, from simple sites to complex enterprise apps, this talk explores what developers should expect from their designers for everything that happens before, during and after loading, and how to ask for it. We’ll look at practical patterns, the trade-offs behind them, and how to document them together so nobody has to guess again.
Stéphanie Walter
Stéphanie is a UX Researcher & Strategist based in Luxembourg with over 15+ years of experience, specialized in enterprise UX, inclusive design and accessibility. She teaches, speaks, and writes about design, UX research, cognitive biases, and the design-dev relationship, among other topics.
When she doesn’t work, she enjoys good tea, bike rides, and drawing illustrations. Her D&D alignment is chaotic neutral, and she is better at keeping her teammates alive in video games than her plants, though she makes an effort. 🌱
The web native APIs
We all know that a speedy website is a very desirable goal. But there is a concept that is not talked about very often : being able to operate without making a request to a server.
What if we could provide websites that have the ability to do their thing mostly while being offline?
In this talk, I’ll show you how I’ve harnessed the native web APIs to implement offline capabilities while minimizing the amount of Javascript to execute in the browser.
Aleth Gueguen
Aleth Gueguen has been an independent software engineer building line of business software for SMBs since 2006.
She takes charge of the entire project, from business diagnosis, scoping, white board workshops, architecture, development, training, maintenance and support.
Her philosophy: use stable and well-known technologies so I can focus on business needs.
When she’s not sailing, she’s on her bike.
Aleth uses her sailboat as a R&D lab to understand what is needed to create resilient and robust software.
Selling Web Performance
Web performance people love data. We bring Core Web Vitals, conversion correlations, and case studies to the meeting, and we often hear “not now.” Why is speed so hard to sell, even when the evidence looks strong?
Martin works on both sides of this problem: as a web performance specialist and as the person who sells PageSpeed.ONE’s work to clients. In this talk, he will share what eight years of conversations with developers, marketers, and business leaders taught him about making the case for speed.
He will look at where familiar arguments fail, what WebPerf can learn from SEO, and why ownership and incentives matter as much as metrics.
You will leave with practical tips to show the problem and turn performance into prioritized work. Backed by community survey insights, you might know more about what actually moves the needle.
Martin Michálek
Martin Michálek is a web performance specialist and CEO of PageSpeed.ONE — a web performance monitoring and consultancy team. With over 25 years in web development, he has worked with dozens of clients ranging from small e-commerce businesses to large global brands — and he also does the sales, giving him a front-row seat to how performance conversations succeed or fail in the real world.
Save a round trip: optimizing for IETF's Happy Eyeballs v3
Connecting to a website used to be simple: resolve a name, open a connection. Not anymore. A browser now races IPv4 against IPv6, HTTP/3 against HTTP/2 and HTTP/1, and even DNS A and AAAA records against the newer HTTPS records. The number of address and protocol combinations keeps growing, and every browser behaves a little differently today. Happy Eyeballs v3, currently being standardized at the IETF, is about to change this.
For website operators the upcoming standard changes the economics of turning on new protocols. With it, the browser falls back to a working option faster and more safely. You can offer e.g. HTTP/3 and improve page load times without paying a connection-setup penalty when a path is broken or blocked. That makes it safe to experiment. I will show what Happy Eyeballs v3's performance impact looks like from the vantage point of millions of Firefox clients. Finally, you will learn how to optimize your own site with savearoundtrip.com, a small tool I built for exactly this.
Max Inden
Max is a software developer interested in networking, distributed systems and type theory. He works at Mozilla on Firefox's networking stack, focusing on HTTP3 and QUIC. Previously he was stewarding the peer-to-peer networking project libp2p, and before that the monitoring system Prometheus and its integration within the Kubernetes orchestrator. To find out more visit max-inden.de.
Beyond the P75
In this deep-dive session, we’ll skip the basics and dive into advanced techniques and fine-tuning strategies to make modern websites lightning-fast. Using real-world data, detailed graphs, and performance metrics, we’ll show how these techniques have helped make scalemates.com the fastest and largest scale modelling website in the world.
You’ll leave with practical, actionable insights to push performance even further. Perfect for those who believe that meeting the Core Web Vitals thresholds for 75% of real-world visits isn’t good enough. Websites should be fast for everyone, across all browsers, devices, connection speeds, and locations.
Tim Vereecke
Tim Vereecke loves speeding up websites and likes to understand the technical and business aspects of WebPerf since 15+ years. He is a Web Performance Architect at Akamai, the inventor of frustrationindex.com and he also runs scalemates.com: the largest (and fastest!) scale modeling website on the planet.
Performance is a journey
Our industry has spent a couple of decades being confident about things that turned out to be wrong – and that's okay. The gap between what we expected and what the data actually shows is one of the subjects of this talk. Underneath every metric, protocol, and best practice we've ever chased is the same challenge: performance is a proxy for how people experience software, and people are not simple enough to sum up in a few metrics.
That's the starting point, not the destination. Harder questions are ahead of us. Questions like what does "fast" even mean when an interface starts answering before it's finished thinking, how much uncertainty will people tolerate from software that's probabilistic instead of deterministic, and why nothing in our observability tooling can tell us when a user is confused instead of content. We don't know what we don't know. This talk is an argument for why that's exciting.
Tammy Everts
Tammy is a digital experience strategist at Palo Alto Networks, where she explores the intersection of technology, human experience, and business outcomes. She has spent more than two decades studying how people use the web, with a particular focus on web performance, UX, and the ways technology shapes human behaviour.
Since 2010, Tammy has researched the relationship between digital experiences and business metrics, helping organizations understand why performance matters – not just as a technical concern, but as a fundamental part of how people experience technology in their everyday lives.
She is the author of Time Is Money: The Business Value of Web Performance (O’Reilly), a distillation of much of her research. She is also co-curator of WPO Stats, a collection of real-world web performance case studies. Tammy is a longtime conference speaker, writer, and researcher who brings a human-centred perspective to complex technology questions.
Tim Kadlec
Tim Kadlec is a performance consultant and trainer focused on building a web everyone can use. He is the author of High Performance Images (O’Reilly, 2016) and Implementing Responsive Design: Building sites for an anywhere, everywhere web (New Riders, 2012), and was a contributing author for Smashing Book #4: New Perspectives on Web Design (Smashing Magazine, 2013), and the Web Performance Daybook Volume 2 (O’Reilly, 2012). He writes about all things web at timkadlec.com. You can find him sharing his thoughts in a briefer format on Twitter at @tkadlec.
Harry Roberts
Harry Roberts is an independent Consultant Web Performance Engineer from the UK. He helps some of the world’s largest and most respected organisations find and fix their site-speed issues.
He is both a Google- and a Cloudinary Media-Developer Expert, and has consulted for clients from the United Nations to the BBC, General Electric to the Financial Times, and a whole host more. He is also co-chair of performance.now(), the web performance conference for professionals.
When not doing client work, he writes, teaches, and speaks about the entire gamut of front-end performance. When not doing work at all, he’s probably out on his bike.