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Capturing a HAR Trace

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This article provides step-by-step instructions on how to capture a HAR trace for troubleshooting purposes.

Details

A .har file (or HTTP Archive format) is used to log a web browser’s interaction with a site and to export detailed performance data about web pages it loads. This article outlines the process to capture the file.

Internet Explorer / Edge

Edge natively produces HAR files. See detailed instructions in the Microsoft site.

  • Open the Network tool in F12 developer tools
  • Reproduce the issue
  • Export captured traffic as a HAR (CTRL + S)

For Internet Explorer, Windows 10 allows capturing HAR natively. (IE on Win 7 exports only to XML/CSV. Fiddler– a free download – can be used to import the XML file when needed.)

  • Open the Network tool in F12 developer tools
  • Press Record (should see Red Square when it’s recording)
  • Reproduce the issue
  • Save button to Export as HAR

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Chrome 

You can record your HTTP session using the Network tab in the Developer Tools in Chrome.  Open the Developer Tools from the menu (Menu > Tools > developer tools), or by pressing Ctrl+Shift+C on your keyboard.

  • Click on the Network tab
  • Look for a round button at the top left of the Network tab. Make sure it is red. If it is grey, click it once to start recording.
  • Check the box next to Preserve log.
  • You can use the clear button (a circle with a diagonal line through it) right before trying to reproduce the issue to remove unnecessary header information
  • Save the capture by right-clicking on the grid and choosing "Save as HAR with Content"

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Firefox

Starting with Firefox 41, HAR files can be created without any additional extension.

  • Start Firefox Developer Tools in Network mode (Top right menu > Developer > Network, or ctrl-shift-Q)
  • Reproduce the issue
  • Save the capture by right-clicking on the grid and choosing "Save all as HAR"
  • Export the capture to a HAR file

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Miscellaneous Notes

Console output can also be interesting.

  • Note screenshot below is from Chrome, which allows Save As
  • If having trouble saving, capturing a screenshot can be helpful.

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