When working on the web, we all end up coming across situations where the experience for the user seems a bit janky. This happens either when you are dogfooding, or the users actually highlight facing that slowness, or you see that for yourself in your performance metrics or tools. What one’d do in such a […]

Introduction You are probably wondering: “What a user centric metric like INP has to do with Puppeteer? Isn’t Puppeteer a tool that lives in the synthetic world?”, or why “Tsvetan, who works on mPulse, a Real User Monitoring system, is messing with synthetic tools?”. The truth is that mPulse and the other Real User Monitoring […]

Last year I came across Jeremy Thomas’ demonstration of Web Design in 4 minutes where he guides the reader step-by-step through beautifying a bland web page. It was powerfully effective, and I began thinking how neat it would be if there was a similar walkthrough based on web performance. WebPerfDemo is the result of that […]

Web developers often spend a lot of time and effort optimizing their web pages to perform better. One of my favorite optimizations is properly setting content expirations to specify how long the client should consider the content to be “fresh”. Here are some good references for caching MDN and RFC 9111. These techniques allow the […]

Some of the times the performance opportunities are easily found and are one of the usual suspects: image size; uncompressed assets; bundle size; preconnect; prefetch; etc. But sometimes the root cause is not as easily found, and those might be on the other side of the server-client boundary. But how can you address and identify […]

If you’re reading this, you probably already know that Interaction to Next Paint (INP) will become the new Core Web Vital metric for responsiveness in March 2024. INP has already been talked about a few times in this year’s Perf Calendar by Brian, Ivailo, and Sander, so if you need a refresher on what it […]

Some things happen in a document during navigating away, right before switching to the new document, especially in same-origin navigation scenarios. We’re not currently measuring them in Navigation Timing. Perhaps we should? Blind spot This came up whe discussing the ongoing deprecation of the unload event. Up until now, we measured the unloadEventStart and unloadEventEnd […]

Introduction to Chrome tracing What is a Chrome trace? If you’re just getting started learning about tracing, you should read this fantastic introduction from the Perfetto tracing documentation. I like their definition: Tracing involves collecting highly detailed data about the execution of a system. A single continuous session of recording is called a trace file […]

Performance engineering, being rather a narrow field by itself, has many well-established specializations. While main generic principles are the same, it is surprising that the overlap in specific skills is rather small and working in one specialization it is easy to miss what is going on in another specialization – making them almost isolated silos. […]

SPA site owners most likely are aware of the gap in Core Web Vitals data for their site. Most metrics (FCP, LCP, FID) are only reported by the browser once, so can’t be measured even if sites were willing to put in extra effort. TTFB is similar, but could potentially be calculated for soft navigations. […]