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While Fiddler may be the original web debugging proxy, it’s never stopped evolving to stay a vital part of developers’, QAs’ and support engineers’ toolboxes.

You probably often hear Progress Telerik Fiddler referred to as the “Original Web Debugging Proxy,” and did you know Fiddler is celebrating its 20-year anniversary?

If this makes you feel old, we are with you. However, Fiddler hasn’t skipped a beat in all these years and has continually evolved to become an integral part of the developers’ toolbox worldwide. Today, we ask you to join us in celebrating Fiddler’s 20th anniversary!

When Did It All Start?

Back in 2003, Eric Lawrence started Fiddler with the idea of simplifying the process of debugging web applications.

In the beginning of the 2000s, there was no easy way to debug applications, uncover issues and network errors, or even monitor incoming and outgoing traffic in real time. Checking what’s under the hood was a time-consuming task.

Like all newcomers, the browser developer tools started out as basic solutions specific to one browser, which resulted in having a learning curve for the different types of information and tools they provided.

This lack of standardization led to the need for a more advanced and unified solution that would incorporate debugging methods no matter the browser or setup you might be using in your work process.

Thanks to Eric, Fiddler (now called Fiddler Classic) was born, which was one of the few web-debugging proxies on the market that gave way to an improved web debugging experience. Fiddler would save teams both time and guesswork and leave more resources for the software development itself.

In the following years, Fiddler became the go-to tool that allowed inspection and modification of traffic through innovative functionalities such as AutoResponder rules, FiddlerScript, breakpoints and many more.

Evolution of Fiddler

Fiddler continued to develop in the years ahead and, eventually, would turn from just one tool into a family of five tools, each aiming to help developers, QAs and support engineers deliver high quality applications and services.

Teams discovered the need for a debugging tool that works on the other operating systems in addition to Windows. That’s when the Mono version was created, which was the first version of Fiddler Classic for macOS and Linux. With the rise of developers operating on macOS and due to performance and stability issues with the Mono port, Progress decided to invest efforts into a new single solution for all operating systems.


In 2018, a beta version of Fiddler Everywhere was born, and, in 2020, the first official version was released which was cross-platform and included premium features.

Fiddler Today

Fiddler could be associated with a family of multiple products split into three categories:

  • Network debugging proxies – the original Fiddler that became Fiddler Classic, and Fiddler Everywhere
  • Troubleshooting tools – FiddlerCap and Fiddler Jam
  • Embeddable .NET library – FiddlerCore, which stands at the very heart of all Fiddler products

Fiddler Classic is one of the first network debugging proxies that introduced a standardized platform to monitor and debug traffic on Windows, and it is also the original tool that put the beginning of the Fiddler brand. Fiddler Everywhere is its continuation that works on Windows, macOS and Linux, and aims to solve the software debugging challenges of today with extended functionalities and modernized UI.

  • Fiddler Everywhere is focused on delivering multiple options for capturing traffic. System proxy, preconfigured browser instance and preconfigured terminal process are the currently supported approaches, but stay tuned for other even more powerful options coming very soon.
  • We are also looking to expand the protocols and frameworks’ support in the cross-platform product, and the recently introduced TLS and gRPC communication are just the beginning of the journey.
  • Be on the lookout for more Composer improvements as well, that will allow better workflow with APIs and their organization in Fiddler Everywhere.

How Fiddler Works

Fiddler works as a man-in-the-middle proxy that generates a unique certificate authority (CA) per machine. It stands between your application and the internet and helps exchange data sent by the client and received by the server. Upon installing and trusting the Fiddler CA, Fiddler can decode the otherwise encoded HTTPS traffic.

Fiddler as an HTTPS proxy is between client and server. Listed are the steps of communication: 1. Client connect tunnel http to Fiddler. 2. TCP Connection established between fiddler and server. 3. Fiddler 200 ok connection established to client. 4. TLSHandshake Client Hello to Fiddler as server. 5. TLSHandshake  Server Hello from Fiddler as server to client. 6. Client sends HTTP request. 8. TLSHandshake Client Hello Fiddler as client to server. 9. TLSHandshake  Server Hello from server to fiddler as client. 10. Fiddler forwards HTTP request to server. 11. Server sends HTTP response to Fiddler. 12. Fiddler forwards HTTP response to client.

As an intermediate proxy, Fiddler allows you to track incoming and outgoing traffic from any application or device. The detailed information inside helps you deep-dive into what is being sent back and forth to easily debug your applications and avoid potential vulnerabilities or performance issues being released to end users.

Thank You!

Fiddler is recognized by users as an integral part of the software debugging process and its impact still remains significant 20 years later. We are grateful for the continuous support from the Fiddler community, and we encourage you to keep on sharing your feature requests, ideas and challenges, so we can shape together the future of Fiddler!

If you missed our celebratory, all-star live session don’t worry, we’ve got you covered!

Check out the recording here:

Simona Yaneva
About the Author

Simona Yaneva

Simona Yaneva is a part of the Product Management team for the Telerik Fiddler Family of products—Fiddler Everywhere, Fiddler Classic, Fiddler Jam, FiddlerCap and FiddlerCore. She is interested in the variety of areas of work that Product Management covers and the processes that make a product or technology successful and most valuable to users. In her free time, Simona enjoys good food, music and dancing.

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