Proxy for Fiddler

### **Proxy for Fiddler: Step-by-step guide to setting up Upstream Proxy for traffic analysis**

**Fiddler Classic** is a legendary tool in the arsenal of any developer, tester, or security specialist. Its main task is to act as a debugging proxy, intercepting and analyzing all HTTP/HTTPS traffic between your computer and the internet. But what if you need Fiddler itself to access the network through *another, external* proxy server?

This feature is called **Upstream Proxy** or **Gateway**, and it is necessary when you need to:

* **Analyze traffic from a specific GEO:** Check what requests your application sends when launched from Germany or Brazil.
* **Simulate user experience:** See how the site works for a user from another country.
* **Bypass network restrictions:** Work from a corporate network where all traffic must go through a specific gateway.
* **Remain anonymous** while debugging and analyzing requests.

In this guide, we will show you step by step how to configure Fiddler to work through an external proxy server.

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### **Step-by-step configuration of an external proxy in Fiddler**

The process is not complicated, but it requires attention. Fiddler will act as a local proxy for your system, and it, in turn, will route traffic through the external proxy you specify.

#### **Step 1: Collect proxy credentials**

The first and most important step is to make sure you have the complete set of authorization data. These “keys” will allow your application or browser to connect to the proxy server and route traffic through it.

Be sure to prepare the following data:

* **IP address** (host server)
* **Port** for connection
* **Login** and **password** for authorization
* **Protocol type** (HTTP/HTTPS or SOCKS5)

![](/media/mdeditor/proxies_info_en_20251007053220501564.png)
*Fig. 1. This screenshot shows where all the necessary fields for connecting to a proxy server are located in your **CyberYozh App** personal account.*

#### **Step 2: Opening Fiddler settings**

1. Launch Fiddler Classic.
2. In the top menu, go to **" Tools“** -> **”Options..."**.

![](/media/mdeditor/1_20250902074408581924.png)
*Fig. 2. This screenshot shows the main working interface of Fiddler Classic before starting the configuration.*

![](/media/mdeditor/2_20250902074617707159.png)
*Fig. 3. This screenshot shows the first step of the configuration, where you need to select the “Tools” section in the top menu.*

![](/media/mdeditor/3_20250902074748894345.png)
*Fig. 4. This screenshot shows the “Tools” drop-down menu, where you need to select “Options...” to go to the settings.*

#### **Step 3: Go to the Gateway settings**

1. In the “Options” window that opens, go to the **“Gateway”** tab. This is where you configure the external proxy gateway.

![](/media/mdeditor/4_20250902074827027247.png)
*Fig. 5. This screenshot shows the “Options” window, where you need to go to the “Gateway” tab to configure the external proxy server.*

#### **Step 4: Manual proxy configuration**

1. On the “Gateway” tab, select the **“Manual Proxy Configuration”** option.
2. The “Proxy string” field will appear. Fiddler supports complex rules, but a simple format is sufficient for most tasks.

![](/media/mdeditor/5_20250902074951856573.png)
*Fig. 6. This screenshot shows the Gateway tab, where Manual Proxy Configuration mode is enabled for manual data entry.*

#### **Step 5: Enter the address and save**

1. In the “Proxy string” field, enter the address of your proxy server in the format `IP:PORT`.
2. Click **“OK”** to save the settings. Fiddler may require a restart to apply the changes.

![](/media/mdeditor/6_20250902075043227537.png)
*Fig. 7. This screenshot shows the final stage of configuration in Fiddler: the IP address and proxy port are entered in the “Proxy string” field, after which you need to click “OK”.*

#### **Step 6: Authorization in the browser**

Now comes the most interesting part. Fiddler has started redirecting traffic through the proxy you specified.

1. Open any browser (it should be configured to use system proxies, which is the default behavior).
2. When you try to visit any website, the browser will display an authorization window.
3. **Important:** Fiddler is asking you for your **login and password for the external proxy server** in order to pass them on. Enter your credentials.

![](/media/mdeditor/7_20250902075237487788.png)
*Fig. 8. This screenshot shows the system authorization window that appears in the browser. At this stage, the fields for the username and password are still empty.*

![](/media/mdeditor/8_20250902075320362363.png)
*Fig. 9. This screenshot shows the process of entering credentials (username and password) from an external proxy server in the authorization window.*

#### **Step 7: Verify the result**

1. After successful authorization, the page will load.
2. Go to any website to check your IP (for example, `browserleaks.com/ip`).
3. Make sure that the IP address and geolocation displayed match the data of your external proxy server. If you are using rotating residential proxies, the IP address may change, but the geolocation should remain the same.

![](/media/mdeditor/9_20250902075416596499.png)
*Fig. 10. This screenshot shows the final result. The browserleaks.com website confirms that the browser is working through an external proxy by displaying its IP address and geolocation.*

**Done!** Now all traffic intercepted by Fiddler will pass through the proxy server you specified, and you will be able to analyze requests as if you were in another part of the world.

### **😎 Pro tip: HTTPS traffic**

Keep in mind that in order to fully analyze **HTTPS traffic**, Fiddler must decrypt it. To do this, in the settings (“Tools” -> “Options...” -> ‘HTTPS’), you need to enable the **“Decrypt HTTPS traffic”** option and add the Fiddler root certificate to the trusted certificates.

![](/media/mdeditor/11_20250902075911761172.png)
*Fig. 11. This screenshot shows the Fiddler settings window, “HTTPS” tab, where you need to enable the “Decrypt HTTPS traffic” option to decrypt secure traffic.*

### **Conclusion**

Configuring Upstream Proxy transforms Fiddler from a powerful debugger into a universal tool for geo-dependent testing and analysis. This feature is indispensable for anyone working on international projects who wants to understand how their applications behave in different network conditions.

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