Fiddler Classic 5.0.20244.10953 for Windows: FAQ

Fiddler Classic 5.0.20244.10953 is a free web debugging proxy for Windows, developed by Progress Telerik. Developers and testers download Fiddler Classic for Windows to see exactly what a browser or app sends to a server and what comes back.

What is Fiddler Classic?

Fiddler sits between your applications and the internet as a local proxy. Every web request that passes through it is recorded in a session list: the address, the method, the status code, the headers and the body of the request and response. You can click a session and read it in various views, from raw text to decoded images and formatted JSON. That makes it possible to find out why a page loads slowly, which request fails, what cookies a site sets or what an app sends in the background. Beyond watching, Fiddler can change traffic: set breakpoints, edit a request before it leaves, replay it later, or answer requests with prepared responses to test how an app handles errors. It is a tool for web developers, QA engineers, support staff and curious power users, and it has been a standard part of many developers' toolkits for years. The name Classic separates it from newer Fiddler products that exist alongside it.

How do I install and start using it?

1. Get the installer through the official Fiddler page.
2. Run setup and start Fiddler; it registers itself as the system proxy while it is capturing.
3. Open a browser and load a site: requests appear in the session list.
4. To read HTTPS traffic, enable HTTPS decryption in the options and trust Fiddler's root certificate when asked.

Is it safe to use?

The tool is legitimate, but HTTPS decryption works by installing a root certificate that lets Fiddler read encrypted traffic. Only enable it on your own computer, and remove the certificate when you no longer need it. Captured sessions can contain passwords and tokens, so do not share saved capture files without cleaning them. Use Fiddler only on traffic you are allowed to inspect.

What are the requirements?

Fiddler Classic runs on Windows and relies on the .NET Framework. No special hardware is required; the program is small, about 4.45 MB according to catalogue data.

Is it free?

Yes, Fiddler Classic is freeware.

Why does my internet stop working after closing it?

If Fiddler closes unexpectedly, the system proxy setting may stay pointed at it. Start Fiddler again and close it normally, or reset the proxy in Windows settings.

What are the pros and cons?

• Pro: detailed view of every request and response.
• Pro: can modify, replay and mock traffic.
• Pro: free.
• Con: Windows only.
• Con: HTTPS inspection requires care with certificates.

What are the alternatives?

On our site, Wireshark analyses network traffic at a lower level, and NetLimiter shows which programs use the connection. For HTTP debugging on Windows, Fiddler Classic is the main tool we list.