Fiddler, bilgisayarınız ile http(ler) arasındaki trafiği kaydeden bir web hata ayıklama yazılımıdır. Program bünyesinde güçlü bir olay tabanlı yazılım altsistemi barındırıyor ve bu alt sistemin herhangi bir .NET dilinin uzantısı olarak kullanılmasına izin veriyor.

Fiddler is a Web Debugging Proxy which logs all HTTP(S) traffic between your computer and the Internet. Fiddler allows you to inspect traffic, set breakpoints, and "fiddle" with incoming or outgoing data. Fiddler includes a powerful event-based scripting subsystem, and can be extended using any .NET language.

Fiddler is freeware and can debug traffic from virtually any application that supports a proxy, including Internet Explorer, Google Chrome, Apple Safari, Mozilla Firefox, Opera, and thousands more. You can also debug traffic from popular devices like Windows Phone, iPod/iPad, and others.