This step-by-step article describes how to create and how to
edit the Web.config file. The Web.config file defines the behavior of ASP.NET
applications. The .NET Framework, including ASP.NET, uses XML-formatted .config
text files to configure applications. This is a departure from conventional
registry and metabase configuration mechanisms. Currently there is no Microsoft
Management Console (MMC) snap-in or other Microsoft-provided administration
tool for creating and for modifying .config files.
Add Configuration Settings to the Web.config File
Most ASP.NET applications come with a prebuilt Web.config file
that can be edited with any text editor such as Notepad. Generally, Web.config
files contain comments that make editing the file self-explanatory. However,
you may have to add configuration items to a Web.config file that does not
already have the configuration item defined. To add a standard configuration
item to a Web.config file, follow these steps:
- Open the Machine.config file in a text editor such as
The Machine.config file is located in the
- In the Machine.config file, locate the configuration
setting you want to override in your Web.config file. When the element is more
than one line, the element starts with an
<element_name> line, and ends with
</element_name>. The element may also be
self-closing and may look similar to <element_name
attribute1=”option” attribute2=”option” />. Note that white
space is ignored. Therefore, the element may span multiple lines. The element
may be preceded by a comment. The comment is contained inside
<!-- and --> markings. The <trace> configuration element example that follows is an example of a
self-closing element. The <trace> configuration element example has multiple attributes, spans
multiple lines, and has a comment at the beginning.
enabled="[true|false]" - Enable application tracing
localOnly="[true|false]" - View trace results from localhost only
pageOutput="[true|false]" - Display trace ouput on individual pages
requestLimit="[number]" - Number of trace results available in trace.axd
traceMode="[SortByTime|SortByCategory]" - Sorts trace result displays based on Time or Category
- Copy the whole configuration element and any beginning
comment to the Clipboard.
- Determine how the element is nested in the Machine.config
The Machine.config file is hierarchical, and configuration
elements are nested in other elements. When you copy a configuration element
from the Machine.config file to the Web.config file, you must nest that
configuration element in the same element that it was copied from. To determine
the element of the Machine.config file that the configuration element is
contained in, scroll up in the Machine.config file until you find an element
that is opened, not closed. The containing element is simple to identify
because higher-level elements have less indentation.
configuration items are contained in the <system.web> element. The end of the element (</system.web>) must be placed after your configuration element.
the element that your configuration element is contained in. You must paste
that element in the same element in the Web.config file. A configuration
element may be nested in multiple elements. You must create all higher-level
elements in the Web.config file.
- Close the Machine.config file and then use your text editor
to open the Web.config file in the root directory of your ASP.NET
- Paste the configuration element between the beginning and
the end of the element that you identified in step 4.
For example, if
the configuration item is contained in the <system.web> element, the configuration item must be pasted immediately after
the opening line of the <system.web> element and before the </system.web> closing line.
- Modify the configuration element in the Web.config file to
override the Machine.config setting for that application.
setting applies to the folder that contains the Web.config file and all
For additional information, click the
following article numbers to view the articles in the Microsoft Knowledge Base:
How To Create the Web.config File
for an ASP.NET Application
How To Deploy Applications That Are Built on the .NET Framework
For more information about ASP.NET configuration and the
format of ASP.NET configuration files, see the .NET Framework SDK documentation
or visit the following Microsoft Web sites:http://msdn2.microsoft.com/en-us/library/aa719558(VS.71).aspx