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Fiddler - Frequently asked questions

Q: Can I change the Text Editor used by Fiddler to something other than Notepad?

A: Yes. 

  • Close Fiddler.
  • Run RegEdit
  • Navigate to HKCU\Software\Microsoft\Fiddler2
  • Add a new REG_SZ named TextEditor
  • Set the new registry value to the path to your text editor.

Q: Can I change the file comparison tool used by Fiddler to something other than WinDiff?

A: Yes. 

  • Close Fiddler.
  • Run RegEdit
  • Navigate to HKCU\Software\Microsoft\Fiddler2
  • Add a new REG_SZ named CompareTool
  • Set the new registry value to the path to your text comparison tool.

Q: I like to navigate around a site then do a "search" for a text on all the logged request/responses. I was curious if Fiddler automatically decompressed gzipped responses during search?

A: Fiddler does not decompress during searches by default, since it would need to keep both the compressed and decompressed body in memory (for data integrity reasons).

For now, simply click Rules > Remove All Encodings and Fiddler will decompress all responses as they come in. If you've already received compressed sessions and want to decompress them in bulk, select the sessions in the list, right-click, and choose Decode Selected Sessions from the context menu.  Then perform your search.

Q: Are there any limitations in Fiddler2?

A: There are a few minor limitations in the HTTPS code:

  • The Request Builder tab cannot yet generate HTTPS requests.
  • HTTPS decryption does not work with authenticating upstream gateway proxy.
  • HTTPS decryption does not play nicely with client socket reuse when there is an upstream gateway.

Q: The HTTPS protocol was designed to prevent traffic viewing and tampering.  Given that, how can Fiddler2 debug HTTPS traffic?

A: Please see the topic Decrypting HTTPS traffic with Fiddler2.

Q: I have another problem.

A: Check the Known Issues or ask in the community!