Zoompf's Web Performance Blog

Note: Archived Content

This is the archived version of the Zoompf blog. Since our acquisition by Rigor, all our new research and posts on web performance are being published on The Rigor Blog

WebPageTest Found a Performance Problem? Fix It Using Zoompf HAR Import!

 Mark Isham on August 25, 2015. Category: announcements

The HAR (aka “HTTP Archive”) file format is a JSON representation of all the content loaded by your browser to render a particular URL. HAR files contain lists of resources requested (CSS, Javascript, images, etc.), the order they were requested, how long it took to download them, and more. The HAR file format is evolving to become the universal communication language between web performance tools. (MaxCDN has a good overview article here).

What you may not know, though, is many of the performance tools you use today can export HAR files as outputs.

For example in Chrome: load any URL, right click anywhere on the page to Inspect Element, click the Network tab, and then right click again to Save as HAR with Content.


Or in WebPageTest, simply click the Export HTTP Archive option in the upper-right corner after you run a new test.


And of course many other tools like Firebug, Zoompf and Rigor also export har files.

Why is this important?

While .har files (and the correspondingly rendered waterfall charts) are quite valuable in identifying performance bottlenecks with your page load resources, they suffer from one key drawback: they don’t help you actually fix the problems. This is where Zoompf comes in.

HAR File Import

Today I’m pleased to announce another great feature for our Web Performance Optimizer beta: HAR file imports!

As users of Zoompf already know, the Zoompf WPO tool analyzes the content of your site for over 400 causes of slow performance, providing detailed step by step instructions on how to resolve each problem. This level of analysis answers the “what’s next?” question. After you find performance slowdowns on your site using WebPageTest or Chrome Dev Tools, you still need to figure out how fix the problems. The Zoompf HAR import can give you that insight.

Here’s how it works.

First, using your favorite waterfall tool of choice, export your initial results to a HAR file. Now, fire up Zoompf WPO and select the New Performance Test option.

From there, select Create New Test, click Advanced, and then HAR File.


You’ll now be prompted to upload that HAR file, or import directly from a hosted URL. Optionally expand the Scanner Options section to further customize your analysis (for example, applying one of our new Defect Check Policies) and then click Start Test to begin the analysis.

The Zoompf performance analyzer will then analyze the content in that HAR file and run its suite of performance defect checks against the specific content in that file, as it was originally captured. This is a great way to analyze “point in time” results that you may have only intermittently seen when debugging with other tools like WebPageTest.

When the analysis is complete, you’ll see a wealth of new information about those HAR file results, including a new interactive waterfall chart that shows all the Performance Defects causing each of the bottlenecks in your results:




Using the HAR Import feature is a great way to chase down those hard to fix performance defects. After you identify a performance bottleneck using WebPageTest, Chrome or Rigor, then just import those HAR results into Zoompf to find out what caused that bottleneck and how you can fix the problem!

If you’d like to learn more about Zoompf Web Performance Optimizer, contact us to schedule a demo. Want to see how your site is performing right now? Try our free performance report.



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