Paul Calvano is a Performance Architect at Etsy, where he helps optimize the performance of their online marketplace.
Many websites use cloud storage as part of how they deliver static content to end users. However using these services without a CDN in front of them has the potential to negatively impact performance. You might be surprised by how many sites do just that - about 8.5% of websites that use a CDN for their primary content, based on HTTP Archive data from January 2026!
You’ve heard it many times - third party content can easily cause an otherwise well performing website to become sluggish and slow. And depending on how this content is loaded, it can also introduce single points of failure (SPOFs). When a large cloud provider or content delivery network (CDN) experiences a disruption, their impacts are felt across the world and often triggers headlines about the…
There’s been a lot of discussion lately around AI crawlers and bots, which are used to train LLMs and/or fetch content on behalf of their users. In the past few weeks I’ve seen blog posts about the amount of traffic from these crawlers, techniques and products to control how and what they can crawl, reports of misbehaving crawlers and more. Ironically, there’s even AI based services to mitigate AI…
It likely comes as no surprise that third party content can be a significant contributor to slow loading websites and poor user experience. As performance engineers, we often need to find ways to balance requirements for their features with the strain that they can put on user experience. Unfortunately, for many sites this becomes a reaction to slowdowns and failures detected in production.
On Monday July 29th, DigiCert announced the need to revoke a large number of certificates due to a bug in domain validation. The CA/B Forum’s strict requirements to revoke these certificates within 24 hours resulted in a pretty busy Monday and Tuesday for a lot of folks. For some others, the deadline was moved to August 3rd due to exceptional circumstances. What remained a mystery was how many…
HTTP compression is a mechanism that allows a web server to deliver text based content using less bytes, and it’s been supported on the web for a very long time. In fact the first web browser to support gzip compression was NCSA Mosaic v2.1 way back in 1993! The web has obviously come a long way since then, but today pretty much every web server and browser still supports gzip compression.
10 years ago, custom web fonts were a niche feature used by ~10% of websites. Today they are used by over 83% of websites! Fonts are generally loaded as a high priority resource, and some sites use techniques such as preload and early hints to get them to load as quickly as possible. Custom web fonts are important to many sites, since rendering with a specific typography is often preferred from a…
In May 2021 Microsoft announced that it would be officially retiring Internet Explorer in favor of the Chromium based Microsoft Edge. Usage for the legacy browser had been very low over the past few years, although many websites have still maintained polyfills for the older browser. In fact a number of my clients have recently told me that supporting IE 11 is required by their business, and is…
If a tree falls in the forest and no one is around, does it make a sound? Likewise, if a web page loads in a background tab then does its load time really matter? As a user, the time it takes for background tabs to load may seem irrelevant since you are unlikely to notice delays. However if you are managing a website and measuring user experience, then it’s important to understand how visibility…
Largest Contentful Paint (LCP) is an important metric that measures when the largest element in the browser’s viewport becomes visible. This could be an image, a background image, a poster image for a video, or even a block of text. The metric is measured with the Largest Contentful Paint API, which is supported in Chromium browsers. Optimizing for this metric is critical to end user experience,…