What is Fiddler?

Fiddler is a Free HTTP debugging proxy server application from Microsoft. Eric Lawrence of Microsoft founded Fiddler; it was launched in 2003.

Uses of Fiddler?

Conventionally, Fiddler is used to tamper the data being sent on the internet. It is an HTTP debugging proxy server application which can also be used to inspect the incoming and outgoing data, and also allows setting break points.Fiddler can also be extended using any .Net language like C#, VB, etc.

What are the Applications of Fiddler?

Fiddler can be used to debug virtual traffic through any application supporting proxy. Fiddler lies between the Client and the Server to capture the traffic generated through the specific Website and categorizes it under different TABS like: Inspectors, Composer, Log, Filters, Timeline, etc.



Features of Fiddler

Check overall Web sessions

User can capture the sessions of any specific domain and get the information regarding that session including:

  • ResponseSize – Size of the response page
  • ClientDoneRequest – Time at which request is sent
  • ClientDoneResponse – Time at which response is sent
  • Result – Code describes the request status
  • URL – Address of the page accessed
  • Host – Host Server address to which request is sent
  • RequestBodySize – Body size of the request in bytes
  • Protocol – Used by the session (HTTP/HTTPS/FTP)

Check Fiddler Inspectors

User can inspect any session captured and explore the details of the Request and Response headers of that session via TABS:

  • Request
    • Headers
    • TextView
    • WebForms
    • HexView
    • Auth
    • Cookies
    • Raw
    • JSON
    • XML
  • Response
    • GetSyntaxView
    • Transformer
    • Headers
    • TextView
    • ImageView
    • HexView
    • WebView
    • Auth
    • Caching
    • Cookies
    • Raw
    • JSON
    • XML

Check statistics of the request

It displays the estimated performance statistics for a selected session to analyze the performance of the request.



  • Fiddler can be used to debug virtual traffic through any application supporting proxy
  • Used for Testing purpose to identify the performance bottlenecks
  • Used for the Load testing
  • Used for Security problems

Supported Operating Systems

Fiddler supports Windows XP, 2003, Vista, 2008, Win7, Win8.

Role of Time Line TAB

To use the Timeline tab, first, highlight the requests in the left pane that you’d like to monitor. Then, you should see how long each element takes to load.

Fiddler for Load/Stress Testing

A free Fiddler plug-in for easy load testing of web applications, StresStimulus plays back HTTP requests recorded in Fiddler to create high concurrency workload on web applications. You can configure virtual users, think time, and number of test iterations or test duration.

After test completion, StresStimulus determines average performance of the test scenario. It breaks down response times of every page between server and network times to identify areas with scalability problems.


This article introduces the basic features of Fiddler with some examples. Fiddler is a very good debugging tool and can be used for testing activities too.