URL Rewriting for IIS – SEO-Friendly URLS for ASP & .Net

We often have clients that host their dynamic sites on IIS which means the file extensions are .asp or .aspx (.Net). This also means the dynamic URLs are SEO unfriendly with many parameters such as: “www.blendermania.com/index.asp?sg=vj6fxvpnixys8vkjk&p=24&c=12″. If this were hosted on a Unix platmform with PHP then a mod_rewrite would be in order to clean up the URL structure making it SEO friendly: “www.blendermania.com/blenders/oster-blender-gx.php”, which is a much nicer URL with descriptive terms. Search engines love that stuff.

So, with a Unix/Apache platform hosting PHP pages, a rewrite is simple. You can read more about it here: Mod_Rewrites.

But for asp and .Net pages it is a bit of a chore. To help with this we have listed a few sources that can help get your URLs rewritten in a jiffy…most of the time. Sometimes is depends if the server has other applications that don’t play well with the ISAPI (Internet Server Application Programming Interface) rewrite module, but you’ll have to ask your host and/or developer about that.

Here are some of the modules that can do URL rewriting on IIS.

Helicon Tech ISAPI_Rewrite

“ISAPI_Rewrite is a powerful URL manipulation engine based on regular expressions. It acts mostly like Apache’s mod_Rewrite, but is designed specifically for Microsoft’s Internet Information Server (IIS). ISAPI_Rewrite is an ISAPI filter written in pure C/C++ so it is extremely fast. ISAPI_Rewrite gives you the freedom to go beyond the standard URL schemes and develop your own scheme.”

QwerkSoft IISRewrite

IISRewrite is a stripped down implementation of Apache’s mod_rewrite modules for IIS. Webmasters who have used Apache’s mod_rewrite in the past will find that much of the configuration and functionality is the same. IISRewrite is compatible with Microsoft’s ISAPI specification and has been tested on Windows NT Server 4.0 running IIS 4 and Windows 2000 Server running IIS 5.


“An ISAPI filter that provides powerful, integrated URL re-writing for IIS. OpUrl has many benefits, including helping to ensure search engines crawl even the dynamic parts of your site. Most search engine crawlers don’t index dynamic pages, e.g. page.asp?item=1 so OpUrl allows you to use static URLs instead. The functionality is very similar to Apache’s mod_rewrite.”

URL Replacer

“The ISAPI filter rewrites/replaces defined parts of URL from browser. It enables url to scripts (.asp, .cgi, .idc) with parameters look like static html pages or specify exact download filename generated by script. You can also create a simple proxy server with IIS and any script engine (.asp,. aspx, …) using URL replacer.”

Microsoft Article on URL Rewriting in ASP.NET

“Examines how to perform dynamic URL rewriting with Microsoft ASP.NET. URL rewriting is the process of intercepting an incoming Web request and automatically redirecting it to a different URL. Discusses the various techniques for implementing URL rewriting, and examines real-world scenarios of URL rewriting. (31 printed pages)”


  1. Very good writeup. This solves a very specific problem which I’m not currently facing so I can’t test any of these out, but I have no doubt that I will run into this in the near future with a couple of client site revamps in the works.

    Can you attest to the ease-of-use/implementation or overall effectiveness of any of these in particular?

    Great info presented clearly. Thanks.

  2. We have only worked with Helicon Tech ISAPI_Rewrite and had good results. Unfortunately our previous host discontinued support and we had to change hosts because of that and went to a Unix Apache server which is much, much better. I can’t speak for any of the others though.

  3. “Most search engine crawlers don’t index dynamic pages, e.g. page.asp?item=1 so OpUrl allows you to use static URLs instead. The functionality is very similar to Apache’s mod_rewrite.”

    I think that’s not true. I have site on IIS and have many pages page.asp?cat=1?id=12345. And all of them are indexed by G.

  4. Damir, that is promotional copy found on that company’s site. Short URLs with one or two parameters are usually indexed and show up in results. But they may suffer by showing further in the search results because of a unfriendly URL. All things being equal it is our belief that a SEO friendly URL will outrank a string-based URL with parameters.

  5. Damir, putting keywords in URLs is usually judicious.

  6. I’d agree with Damir’s point about dynamic url’s and the fact that they are crawled. It’s probably a historical thing but it hasn’t been a problem for quite a while now, particularly with the advent of XML sitemaps.

    I think the benefits of keywords in the url (domain in particular) and then folder/filename is indisputable, but does anyone have any idea if there are any SEO benefits of keywords in request parametrs? For example:


  7. Friendly URLs is definitely important. That’s how we discovered your site via organic search. I love your picture of the kids and Christmas. So cute. an even you have little baby furniture for them!

  8. URL’s are a hugely important factor when it comes to SEO. Tips like these are what make you stand above your competition.


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