Last Updated: 02 Sep 2020 10:28 by ADMIN
Created on: 25 Aug 2020 10:42
Type: Bug Report
Fiddler incorrectly interpreting some int64 numbers


I've the following request response:

    "proId": 98767975948505330

This is correctly displayed in the "Raw Tab", but when switching to the JSON tab, the displayed number is not correct.


Could you fix this ?


Nick Iliev
Posted on: 02 Sep 2020 10:28

Hi Eric,


Thanks for the notice! I've escalated the behavior as a bug (both for the classic Fiddler and Fiddler Everywhere) and the team will look into it in future releases.


Nick Iliev
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Posted on: 31 Aug 2020 14:48

Notably, FiddlerEverywhere will still change numbers:

99999999999999999999 renders as 100000000000000000000


Also, the JSON parser in Fiddler Everywhere will not render anything at all for 

   {   this_is_big: 98767975948505330 }

It requires that you quote the name, like:

   {  "this_is_big": 98767975948505330 } 



Nick Iliev
Posted on: 31 Aug 2020 05:53

Hello Nisalon,


As Eric noticed the issue is indeed a legit limitation related to the JSON parser and larger numbers. I am marking the issue as a valid bug to be fixed in the classic Fiddler. As a side note, I wanted to let you know that the new FIddler Everywhere handles large numbers as expected (the bug is not present)


Nick Iliev
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Posted on: 25 Aug 2020 15:56
Notably, Telerik could fix this by updating the JSON parser (based on an open-source library) but if they do so I hope they add a JSONParseWarning to the JSON tab to warn the user that the values are not interoperable.
Posted on: 25 Aug 2020 15:43

You've encountered a fun limitation in JavaScript; you cannot safely use numbers of that size in JSON.

Your number, 


is significantly larger than the largest integer that can be represented safely in a JavaScript number (which is a floating point value):


    9007199254740991  = MAX_SAFE_INTEGER 


If you want such numbers to be interpreted safely by all clients, you need to send them as strings and serialize/deserialize them as needed.