Thinking about a website’s user experience cannot be limited to just the design of the user interface and people’s interactions with it. From the consumer’s point of view, their experience extends to everything that happens from the moment they first visit the site to when the product or information they seek is delivered.
One important aspect of the user experience, perceived site performance, can be particularly vexing to site users and designers alike. That’s because when a site is slow to download or respond to user actions it causes the visitor to focus on something that is getting in the way of what they are trying to do. The guidance around response times Jakob Nielsen provided in his 1994 book Usability Engineering is still true today, perhaps even more so given people’s increased exposure to broadband internet access at home and work.
Fortunately there are many tools out there for measuring how your site is performing in terms of download speed and response time. Here’s a few free ones I use:
Firebug: The Net tab in the popular Firefox Add-On displays the size and download speed of each of the individual elements that make up a particular web page. It displays the information in a waterfall graph showing when each object’s download begins and ends, allowing you to easily see when a Flash object or other large file may slowing down the site’s perceived performance. This is especially useful if your site has third-party advertising served from a network you don’t control.
YSlow for Firebug: YSlow is an extension to Firebug from the Yahoo! Developer Network. YSlow measures a site’s download performance across 22 categories and provides guidance on how to improve performance. YSlow looks at things like file size, the number of HTTP requests needed to deliver the entire page, and image scaling.
Tamper Data: This Firefox Add-On gives you an extremely granular look at a site’s HTTP and HTTPS requests and responses. You can see file sizes, duration of requests and responses, and HTTP response code your server sends back to browser. This is useful if your site is experiencing slow response times because of requests to third-party content or if there is a problem in your content distribution network.
Bandwidth Place: This website can measure your computer’s upload and download speeds and show if your network connection is creating a bottleneck. If your download speed is comparable to what your site users have, which is often the case for intranet applications, this can help you understand what your audience is experiencing.
For industrial strength monitoring, Keynote Systems and Gomez offer paid services that can monitor download performance and response time from a geographically distributed network of computers that allows you to see how the site is performing from a worldwide perspective.
Keynote and Gomez also offer continuous monitoring services in which intelligent agents repeatedly visit a site from numerous geographically distributed locations and run through a scripted set of actions like performing a search, adding an item to a shopping cart, and checking out. Their services also provide email and SMS text alerting when performance thresholds have been exceeded. Keynote also has a free service, Keynote RedAlert, that can be used for 30 days to test scripted monitoring.