Introduction

Fiddler is an HTTP protocol debugging agent tool that can record and check all HTTP communication between your computer and the internet, set breakpoints, and view all "in and out" Fiddler data (referring to cookies, HTML, JS, CSS, and other files). Fiddler is simpler than other network debuggers because it not only exposes HTTP communication but also provides a user-friendly format.

Use

Fiddler supports breakpoint debugging technology. When you select before request in the software's menu rules automatic breakpoints option, or when these request or response properties match the target's standards, Fiddler can pause HTTP communication and allow modification of requests and responses. This feature is very useful for security testing, but it can also be used for general functional testing, as all code paths can be used for exercises.

By displaying all the HTTP communication, Fiddler can easily demonstrate which pages are used to generate a web page. By counting the page (which is the large box on the left of Fiddler), users can easily use multiple selections to obtain the "total weight" of a web page (page file and related JS, CSS, etc.). You can also easily see how many times a page you have requested, and how many bytes have been converted.
Users can add an Inspector plugin object to write Fiddler extensions in any language under. net. RequestInspectors and ResponseInspectors provide a formatted or specified (user defined) HTTP request and response view.
In addition, by exposing HTTP headers, users can see which pages are allowed to be cached on the client or proxy side. If a response does not include a Cache Control header, it will not be cached on the client.
Similar tools include: httpwatch, firebug, and wireshark.

Result

The result column is the code indicating whether the request was successful. The most common codes include:
200- Success. The request has been sent and the response has been successfully received.
400- Bad request. When the destination server receives a request but does not understand the details and is unable to process it.
404- Page not found. If the target API has been moved or updated but backward compatibility has not been preserved.
500- Internal server error. A fatal error occurred on the server side, and the error was not captured by the service provider.

URL

Refers to the specific page or endpoint (or root URL, if a tunnel is used) being requested. Many backend services use seemingly unfamiliar URLs. For example, docs. live. net: 443 is actually Microsoft OneDrive.
Check the Process column to see which applications are issuing the given request. If you see the Explorer process, it refers to Windows Explorer (not IE). Windows Explorer is essentially Windows itself, and its traffic is often caused by Windows refreshing live title data.