Tip/Trick: Fix Common SEO Problems Using the URL Rewrite Extension
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by Scott Guthrie
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How to Easily Fix these SEO Problems in 10 minutes (or less) using IIS Rewrite

If you haven’t been careful when coding your sites, chances are you are suffering from one (or more) of the above SEO problems.  Addressing these issues will improve your search engine relevancy ranking and drive more traffic to your site.

The “good news” is that fixing the above 4 issues is really easy using the URL Rewrite Extension.  This is a completely free Microsoft extension available for IIS 7.x (on Windows Server 2008, Windows Server 2008 R2, Windows 7 and Windows Vista).  The great thing about using the IIS Rewrite extension is that it allows you to fix the above problems *without* having to change any code within your applications. 

You can easily install the URL Rewrite Extension in under 3 minutes using the Microsoft Web Platform Installer (a free tool we ship that automates setting up web servers and development machines).  Just click the green “Install Now” button on the URL Rewrite Spotlight page to install it on your Windows Server 2008, Windows 7 or Windows Vista machine:

Once installed you’ll find that a new “URL Rewrite” icon is available within the IIS 7 Admin Tool:

Double-clicking the icon will open up the URL Rewrite admin panel – which will display the list of URL Rewrite rules configured for a particular application or site:

Notice that our rewrite rule list above is currently empty (which is the default when you first install the extension).  We can click the “Add Rule…” link button in the top-right of the panel to add and enable new URL Rewriting logic for our site. 

Scenario 1: Handling Default Document Scenarios

One of the SEO problems I discussed earlier in this post was the scenario where the “default document” feature of IIS causes you to inadvertently expose two URLs for the same content on your site.  For example:



We can fix this by adding a new IIS Rewrite rule that automatically redirects anyone who navigates to the second URL to instead go to the first one.  We will setup the HTTP redirect to be a “permanent redirect” – which will indicate to search engines that they should follow the redirect and use the new URL they are redirected to as the identifier of the content they retrieve. 

Let’s look at how we can create such a rule.  We’ll begin by clicking the “Add Rule” link in the screenshot above.  This will cause the below dialog to display:

We’ll select the “Blank Rule” template within the “Inbound rules” section to create a new custom URL Rewriting rule.  This will display an empty pane like below:

Don’t worry – setting up the above rule is easy.  The following 4 steps explain how to do so:

Step 1: Name the Rule

Our first step will be to name the rule we are creating.  Naming it with a descriptive name will make it easier to find and understand later.  Let’s name this rule our “Default Document URL Rewrite” rule:

Step 2: Setup the Regular Expression that Matches this Rule

Our second step will be to specify a regular expression filter that will cause this rule to execute when an incoming URL matches the regex pattern.   Don’t worry if you aren’t good with regular expressions - I suck at them too. The trick is to know someone who is good at them or copy/paste them from a web-site. 

Below we are going to specify the following regular expression as our pattern rule:


This pattern will match any URL string that ends with Default.aspx. The "(.*?)" matches any preceding character zero or more times. The "/?" part says to match the slash symbol zero or one times. The "$" symbol at the end will ensure that the pattern will only match strings that end with Default.aspx. 

Combining all these regex elements allows this rule to work not only for the root of your web site (e.g. http://scottgu.com/default.aspx) but also for any application or subdirectory within the site (e.g. http://scottgu.com/photos/default.aspx.  Because the “ignore case” checkbox is selected it will match both “Default.aspx” as well as “default.aspx” within the URL.

One nice feature built-into the rule editor is a “Test pattern” button that you can click to bring up a dialog that allows you to test out a few URLs with the rule you are configuring:


Above I've added a “products/default.aspx” URL and clicked the “Test” button.  This will give me immediate feedback on whether the rule will execute for it. 

Step 3: Setup a Permanent Redirect Action

We’ll then setup an action to occur when our regular expression pattern matches the incoming URL:

In the dialog above I’ve changed the “Action Type” drop down to be a “Redirect” action.  The “Redirect Type” will be a HTTP 301 Permanent redirect – which means search engines will follow it.

I’ve also set the “Redirect URL” property to be:


This indicates that we want to redirect the web client requesting the original URL to a new URL that has the originally requested URL path - minus the "Default.aspx" in it.  For example, requests for http://scottgu.com/default.aspx will be redirected to http://scottgu.com/, and requests for http://scottgu.com/photos/default.aspx will be redirected to http://scottgu.com/photos/

The "{R:N}" regex construct, where N >= 0, is called a regular expression back-reference and N is the back-reference index. In the case of our pattern "(.*?)/?Default\.aspx$", if the input URL is "products/Default.aspx" then {R:0} will contain "products/Default.aspx" and {R:1} will contain "products".  We are going to use this {R:1}/ value to be the URL we redirect users to. 

Step 4: Apply and Save the Rule

Our final step is to click the “Apply” button in the top right hand of the IIS admin tool – which will cause the tool to persist the URL Rewrite rule into our application’s root web.config file (under a <system.webServer/rewrite> configuration section):

                 <rule name="Default Document" stopProcessing="true"> 
                     <match url="(.*?)/?Default\.aspx$" /> 
                     <action type="Redirect" url="{R:1}/" /> 

Because IIS 7.x and ASP.NET share the same web.config files, you can actually just copy/paste the above code into your web.config files using Visual Studio and skip the need to run the admin tool entirely.  This also makes adding/deploying URL Rewrite rules with your ASP.NET applications really easy.

Step 5: Try the Rule Out

Now that we’ve saved the rule, let’s try it out on our site.  Try the following two URLs on my site:



Notice that the second URL automatically redirects to the first one.  Because it is a permanent redirect, search engines will follow the URL and should update the page ranking of http://scottgu.com to include links to http://scottgu.com/default.aspx as well.

Scenario 2: Different URL Casing

Another common SEO problem I discussed earlier in this post is that URLs are case sensitive to search engines on the web.  This means that search engines will treat the following links as two completely different URLs:



We can fix this by adding a new IIS Rewrite rule that automatically redirects anyone who navigates to the first URL to instead go to the second (all lower-case) one.  Like before, we will setup the HTTP redirect to be a “permanent redirect” – which will indicate to search engines that they should follow the redirect and use the new URL they are redirected to as the identifier of the content they retrieve.

To create such a rule we’ll click the “Add Rule” link in the URL Rewrite admin tool again.  This will cause the “Add Rule” dialog to appear again:

Unlike the previous scenario (where we created a “Blank Rule”), with this scenario we can take advantage of a built-in “Enforce lowercase URLs” rule template.  When we click the “ok” button we’ll see the following dialog which asks us if we want to create a rule that enforces the use of lowercase letters in URLs:


When we click the “Yes” button we’ll get a pre-written rule that automatically performs a permanent redirect if an incoming URL has upper-case characters in it – and automatically send users to a lower-case version of the URL:

We can click the “Apply” button to use this rule “as-is” and have it apply to all incoming URLs to our site. 

Because my www.scottgu.com site uses ASP.NET Web Forms, I’m going to make one small change to the rule we generated above – which is to add a condition that will ensure that URLs to ASP.NET’s built-in “WebResource.axd” handler are excluded from our case-sensitivity URL Rewrite logic.  URLs to the WebResource.axd handler will only come from server-controls emitted from my pages – and will never be linked to from external sites.  While my site will continue to function fine if we redirect these URLs to automatically be lower-case – doing so isn’t necessary and will add an extra HTTP redirect to many of my pages. 

The good news is that adding a condition that prevents my URL Rewriting rule from happening with certain URLs is easy.  We simply need to expand the “Conditions” section of the form above

We can then click the “Add” button to add a condition clause.  This will bring up the “Add Condition” dialog:


Above I’ve entered {URL} as the Condition input – and said that this rule should only execute if the URL does not match a regex pattern which contains the string “WebResource.axd”.  This will ensure that WebResource.axd URLs to my site will be allowed to execute just fine without having the URL be re-written to be all lower-case.

Note: If you have static resources (like references to .jpg, .css, and .js files) within your site that currently use upper-case characters you’ll probably want to add additional condition filter clauses so that URLs to them also don’t get redirected to be lower-case (just add rules for patterns like .jpg, .gif, .js, etc).  Your site will continue to work fine if these URLs get redirected to be lower case (meaning the site won’t break) – but it will cause an extra HTTP redirect to happen on your site for URLs that don’t need to be redirected for SEO reasons.  So setting up a condition clause makes sense to add.

When I click the “ok” button above and apply our lower-case rewriting rule the admin tool will save the following additional rule to our web.config file:

                <rule name="Default Document" stopProcessing="true"> 
                    <match url="(.*?)/?Default\.aspx$" /> 
                    <action type="Redirect" url="{R:1}/" /> 
                <rule name="Lower Case URLs" stopProcessing="true"> 
                    <match url="[A-Z]" ignoreCase="false" /> 
                    <conditions logicalGrouping="MatchAll"
                    <add input="{URL}" pattern="WebResource.axd" negate="true" /> 
                    <action type="Redirect" url="{ToLower:{URL}}" /> 

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