Modifying Traffic

Fiddler Everywhere provides a powerful debugging techniques for editing and mocking the captured traffic.

Composing Requests

Instead of testing your API or a website through the UI and making multiple clicks, you can reload the desired session in the Composer tab, make edits to the desired values, and re-execute the request.

To load and modify a session through the Composer:

  1. Set Live Traffic to Capturing and make the request. As a result, the session is captured and displayed in the Live Traffic list.

  2. Select the desired session and right-click to open the context menu. From the context menu, select Edit in Composer. Alternatively, select the session and use the keyboard shortcut by pressing the E key.

    Edit in Composer

  3. The session opens in a new Composer window and then you can change the desired values. For example, change the data payload, modify the headers, test the authentication, and so on.

    Change the loaded request values in new Composer windows

    To modify a header, select it and change the needed key-value pair. You can add a new header by using the top key-value row. By default, the top key-value row is empty and can receive new values. Once you have modified or added a new header, click the confirmation button (a tick) to the right to apply the changes.

  4. Click Execute.

This approach enables you to modify an existing request in the same way your application does it. In the Live Traffic list, you can find the newly executed request and the response from the server.

Using Rules

One of the most powerful features in Fiddler Everywhere resides in the Rules tab. You can create your own rules that change HTTP Requests & Responses on-the-fly based on different criteria. The rules can combine multiple criteria and apply single or multiple actions, allowing you to mock real-life scenarios with few clicks. Learn more about the Rules tab capabiliees in the following article:

Additional Resources