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Fiddler

Key Features

Customizable Free Tool

  • Extending Fiddler with FiddlerScript and .NET code

    Web developers can easily extend Fiddler using the .NET Framework. There are two way to go about it: create either Custom Rules or Inspectors.


    Read more in the Documentation

  • Fiddler extensions and add-ons

    Fiddler’s rich extensibility model enables developers to add powerful new features to Fiddler via easily installed add-ons. Among the most popular 3rd party extensions are the ones that enhance Fiddler’s ability to test the performance and security characteristics of web applications.


    See full list of Fiddler add-ons

  • Adding inspectors

    An alternative way to extending and customizing Fiddler according to your needs is by adding Inspectors which can be written in any .NET language. Inspectors can be read-only or read-write. If an Inspector is read-write, you can use it to modify the HTTP request or response before the server or the client receives it. The changes you make while the paused at a breakpoint are committed automatically by the Inspector.


    A quick list of commonly used request/response Inspector types includes:


    Request Inspectors

    [RW] Headers—Shows request headers and status.

    [RW] TextView—shows the request body in a text box.

    [RO] XML—shows the request body as an XML DOM in a tree view.

     

    Response Inspectors

    [RW] Transformer—Removes GZIP, DEFLATE, and CHUNKED encodings for easier debugging.

    [RW] Headers—Shows response headers and status.

    [RO] ImageView—shows the response body as an Image. Supports all .NET image formats.

    [RO] XML—shows the response body as an XML DOM in a tree view.

  • Creating rules

    Fiddler supports a rich extensibility model which ranges from simple FiddlerScript to powerful Extensions which can be developed using any .NET language.


    Rules are the primary way to extend Fiddler – in essence, it’s a JavaScript file that contains commands to extend Fiddler’s UI, or modify the session request and response. You can extend and customize the rules menu – for example the sub-menu items like user agents get populated from your JavaScript file.

    There are various rules that you can start using out of the box:

    • Hide image requests – control if you’d like to see returned images in the session list
    • Hide connects – decide if you’d like to see the original, raw connection to the server
    • Automatic breakpoints – use if you’d like to have Fiddler automatically breakpoint before/after each request and response.
    • Remove all encodings – removes all HTTPs request/response encodings
    • Hide 304s – gives you the option to hide all HTTP responses that have not been modified
    • Choose among user-agents or set a custom value

    Alternatively, you can create your own custom rules by using FiddlerScript.


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