(formerly "Request Builder")
The Composer allows you to craft custom requests to send to a
server. You can either create a new request manually, or you can
drag and drop a session from the Web Sessions list to create a new request
based on the existing request.
There are two modes for the Composer. In Parsed
mode, you can use the boxes to build up a HTTP(S) request. In Raw
mode, you must type in a properly formatted HTTP request
yourself. Generally, using Parsed Mode is what you want.
The Options tab exposes options that allow you to customize the
behavior of the Composer.
- Inspect Session selects the new session and
activates the Inspectors tab when the request is issued.
- Fix Content-Length Header adjusts the value of
the Content-Length request header (if present) to
match the size of the request body.
- Follow Redirects causes a HTTP/3xx redirect to
trigger a new request, if possible. The Composer will follow up
to fiddler.composer.followredirects.max default redirections.
- Automatically Authenticate causes Fiddler to
automatically respond to HTTP/401 and HTTP/407 challenges that use
NTLM or Negotiate protocols using the current user's Windows
Tips and Tricks
- Use drag-and-drop from the Session List to create a new request based on a
- Use a # character in the RequestURL to be prompted for
a series of sequentially-numbered URLs to download. If you enter a leading
0 (zero) before the "Start At" value, then all numbers will be padded
with leading zeros (if necessary) to get to that width.
instance, if you have the URL http://www.example.com/#/?a=#,
and enter the Start At value as 08 and the End At
value as 11, the Composer will request the
- Shift+Click the Execute button to immediately break the new request for
further editing using Fiddler's Inspectors
- Add a dummy header Fiddler-Encoding: base64 and
encode your body using base64 if it contains any binary data. Fiddler
will decode the data before transmitting it to the server.
- Add a dummy header Fiddler-Host:
targettesthost if you would like Fiddler to send
your request to the specified server (http://targettesthost, in this
case) while retaining the URL and host header specified elsewhere in
the request. This is a convenience method that setS the
X-OverrideHost, X-IgnoreCertCNMismatch and
X-OverrideGateway flags on the new Session, removing
the dummy header before contacting the specified server.
- Click the Upload File link to have the composer
inject one or more local files into the request body as it is sent to
If you would like the uploaded file to be sent as
base64 (as you might in an XML post body) insert the
token base64 into the string. For instance:
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