**Fiddler** is a powerful HTTP/HTTPS traffic analyzer for debugging network activity between applications and the web. It helps developers inspect requests, diagnose performance issues, and test how traffic behaves through proxy connections or under various network conditions.
## **Get your Squid Proxy credentials** Before configuring Fiddler, make sure you have the following: - Proxy IP address (e.g., `123.456.78.90`) - Port (commonly `8800`) - Username and password (_for user/pass authentication_) **OR** Make sure your current IP is whitelisted (_for IP-auth plans_)
## **Download and launch Fiddler** 1. Visit the official Fiddler site: [https://www.telerik.com/fiddler](https://www.telerik.com/fiddler) 2. Download **Fiddler Classic** (for Windows) or **Fiddler Everywhere** (cross-platform) 3. Install and launch the application
## **Configure Squid Proxies in Fiddler** You can route Fiddler’s own outgoing traffic through your Squid Proxy to inspect how your apps, scrapers, or browsers behave when using proxies. ### **For Fiddler Classic:** Go to: **`Tools > Options > Gateway`** Under **Use custom proxy**, enter: ```plaintext Host: Your Squid Proxy IP Port: Your Squid Proxy Port ``` If using user/pass authentication: - Check: **"Authenticate using the following credentials"** - Enter your **username and password**
### **For Fiddler Everywhere:** Go to: **`Settings > Connections`** Toggle **Manual Configuration** under **Upstream Proxy**, then enter: ```plaintext Authenticated Format: http://username:password@ip:port IP-based Access Format: http://ip:port ``` Save and restart Fiddler if needed. ✅ All Fiddler traffic will now be routed through your Squid Proxy.
## **Capture and inspect browser, app, or device traffic in Fiddler** Use Fiddler as a proxy to inspect traffic from mobile or desktop apps: 1. **On your mobile device:** - Set Wi-Fi proxy to your computer’s IP on port `8888` 2. In Fiddler, enable HTTPS decryption: **`Tools > Options > HTTPS`** 3. Trust and install the Fiddler SSL certificate on your device ✅ This allows inspection of all HTTPS requests sent via Squid Proxies.
## **Test proxy routing in Fiddler** To confirm traffic is going through your Squid Proxy: 1. Open a browser and visit: - [https://ipinfo.io](https://ipinfo.io) or [https://whatismyip.com](https://whatismyip.com) 2. In Fiddler logs, check the request 3. Confirm the returned IP matches your Squid Proxy IP
## **Common use cases for Fiddler with Squid Proxies** | Use Case | Benefit | |-----------------------|---------------------------------------------------------------------| | Proxy debugging | Confirm that Squid Proxies are routing and authenticating correctly | | API testing | Inspect request headers, payloads, and responses through proxies | | Geo testing | Simulate traffic from different locations using residential proxies | | Rate-limiting analysis| Detect when and why a server is blocking or throttling your requests|
## **Rotate proxies in Fiddler** If you're using rotating residential proxies: ```plaintext Rotating Endpoint Example: http://res.squidproxies.com:PORT ``` - Set as your **upstream proxy** - Each new connection will use a different IP - Combine with session analysis for deeper traffic behavior insights For sticky sessions, contact Squid Proxies support for dedicated session ports.
## **Troubleshooting proxy issues in Fiddler** - **Fiddler not capturing traffic?** → Make sure apps/browsers route through `localhost:8888` - **Can’t decrypt HTTPS?** → Enable HTTPS inspection and trust SSL certificate - **Proxy authentication issues?** → Double-check proxy format and login credentials - **Wrong IP detected?** → Verify upstream proxy settings and browser routing
## **Best practices for Fiddler proxy setup** - Start with IP checkers (https://ipinfo.io, https://whatismyip.com) before large-scale testing - Use **Fiddler AutoResponder** or **Breakpoints** for debugging sessions - Rotate proxies to simulate distributed access patterns - Use **residential IPs** for geo-sensitive or mobile app testing
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**More Guides:** - [Choose your authentication method](https://www.squidproxies.com/developer-docs/dev-getting-started/choose-your-authentication-method) - [Avoiding blocks at scale](https://www.squidproxies.com/developer-docs/dev-advanced-guides/avoiding-blocks-at-scale)