Mocking Server Response

One of the most powerful features of the Fiddler Everywhere client is the AutoResponder - a tool for mocking server responses and simulating various real-life scenarios. With AutoResponder, you can create rules, which will automatically trigger to a specific request (that covers the criteria set in the rule). Mocking a server response is as easy as setting as enabling AutoResponder, setting a rule, and executing the request (that will trigger the rule).

Creating AutoResponder Rule

To create and test your first AutoResponder rule follow these steps:

  1. Open the Fiddler Everywhere client and switch the Live traffic to Capturing mode.

  2. Select the AutoResponder tab and create your rule.

    AutoResponder button

  3. In the MATCH field, enter your match criteria. For this example, in the lines below, you will find a simple rule that matches ALL requests ending with PNG (the rules are created while using regular expressions).

    regex:(?inx).+\.png$ #Match strings ending with PNG

    AutoResponder button

    The following basic example is creating a MATCH rule that will modify all requests that are ending with PNG. In most cases, you would like to mock a response from a request against a specific host. For that case, you could use the EXACT match. See more examples for creating different MATCH conditions.

  4. In the ACTION field, enter the desired action. For this example, in the lines below, you will find a simple action that will drop everything corresponding to the MATCH criteria.


    AutoResponder button

    See more examples for creating actions

  5. Add the rule to the AutoResponder rules list

    AutoResponder button

  6. Enable the AutoResponder

    AutoResponder button

    Once the AutoResponder is turned on (via Enable AutoResponses), the activated rules apply for all incoming/outgoing traffic. If a session does not match any of the specified rules, the Fiddler Everywhere client will generate an HTTP/404 Not Found response. In case, you want unmatched requests to be sent generally to the servers, then activate the Unmatched Requests Passthrough option from the toolbar.

  7. Open the application (e.g., a browser) and execute the request. As a result, if the request contains PNG images, they will be dropped. You have just tested a website against a scenario where the user has disabled all photos.

Additional Resources

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