Using Fiddler for HTTP

Fiddler is a web debugging proxy that logs all HTTP(S) traffic between your computer and the Internet. This lesson will guide you through setting up and using Fiddler effectively to analyze HTTP requests and responses.

1. Download Fiddler from the official website: Fiddler Download.
2. Run the installer and follow the on-screen instructions to complete the installation.
3. Launch Fiddler after installation.

3.1 Starting Fiddler

Open Fiddler, and you will see the main interface displaying a list of captured sessions.

3.2 Capturing Traffic

Fiddler automatically starts capturing HTTP traffic once it is launched. If you wish to stop capturing, click on the “Capture Traffic” button.

3.3 Inspecting HTTP Requests and Responses

Select any session from the list to view detailed information about the request and response.

GET /example HTTP/1.1
Host: www.example.com
User-Agent: Fiddler
Accept: */*
            

The above request can be inspected in the "Inspectors" tab where you can see headers, body, and more.

3.4 Modifying Requests

You can modify requests before they are sent to the server. Right-click on a session, select “Edit in Composer”, make your changes, and then click “Execute”.

4.1 Use Filters

To focus on specific traffic, use filters to exclude unnecessary sessions. This can be done via the “Filters” tab.

4.2 Enable HTTPS Decryption

To analyze HTTPS traffic, enable HTTPS decryption in Fiddler by navigating to Tools > Options > HTTPS and checking the “Decrypt HTTPS traffic” option.