Force URLs to lowercase, especially important for SEO on Windows-based servers, which are case-insensitive; not implementing this rule on Windows servers can lead to duplicate content penalties in search engines.

Add the following rule to your web.config’s <rules> section:

<system.webServer>
	<rewrite>
		<rules>
			<rule name="Convert to lower case" stopProcessing="true">
				<match url=".*[A-Z].*" ignoreCase="false" />
				<action type="Redirect" url="{ToLower:{R:0}}" redirectType="Permanent" />
			</rule>
		</rules>
	</rewrite>
</system.webServer>

For SEO purposes, this type of redirect should be Permanent (301).

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In More Detail

It is vitally important for SEO to avoid duplicate content. From a search engine perspective, two URLs whose sole difference is a single capitalized letter will be interpreted as two distinctly different URLs. On Windows servers, or a web application that treats URLs as case-insensitive, this will result in example.com/mywebpage and example.com/MyWebPage as being two distinctly different urls which return the exact same content; hence, duplicate content penalty.

To help protect your site to be immune to these penalties, it’s best to standardize on all lowercase URLs. Missing those CamelCase or lowerCamelCase URLs? Fine, choose hyphenated urls instead: camel-case and lower-camel-case. They’re just as readable, and actually perform better from an SEO standpoint since they’re tokenized on the hyphens.