You can try this

string str = phrase.ToLower(); //optional str = str.Trim(); str = Regex.Replace(str, @"[^a-z0-9\s_]", ""); // invalid chars str = Regex.Replace(str, @"\s+", " ").Trim(); // convert multiple spaces into one space str = str.Substring(0, str.Length <= 400 ? str.Length : 400).Trim(); // cut and trim it str = Regex.Replace(str, @"\s", "-"); 

Perhaps this question here can help you on your way. It gives you code on how Stackoverflow generates its url's (more specifically, how question names are turned into nice urls.

Link to Question here, where Jeff Atwood shows their code

From your examples, the closest thing I've found (although I don't think it does everything that you're after) is:

My Favorite String Extension Methods in C#

and also:

ÜberUtils - Part 3 : Strings

Since neither of these solutions will give you exactly what you're after (going from the examples in your question) and assuming that the goal here is to make your string "safe", I'd second Hogan's advice and go with Microsoft's Anti Cross Site Scripting Library, or at least use that as a basis for something that you create yourself, perhaps deriving from the library.

Here's a link to a class that builds a number of string extension methods (like the first two examples) but leverages Microsoft's AntiXSS Library:

Extension Methods for AntiXss

Of course, you can always combine the algorithms (or similar ones) used within the AntiXSS library with the kind of algorithms that are often used in websites to generate "slug" URL's (much like Stack Overflow and many blog platforms do).

Here's an example of a good C# slug generator:

Improved C# Slug Generator

You could use HTTPUtility.UrlEncode, but that would encode everything, and not replace or remove problematic characters. So your spaces would be + and ' would be encoded as well. Not a solution, but maybe a starting point

If the goal is to make the string "safe" I recommend Mirosoft's anti-xss libary

There will be no library capable of what you want since you are stating specific rules that you want applied, e.g. $x => x-dollars, x% => x-percent. You will almost certainly have to write your own method to acheive this. It shouldn't be too difficult. A string extension method and use of one or more Regex's for making the replacements would probably be quite a nice concise way of doing it.

e.g.

public static string ToUrl(this string text) { return text.Trim().Regex.Replace(text, ..., ...); } 

Something the Ruby version doesn't make clear (but the original Perl version does) is that the algorithm it's using to transliterate non-Roman characters is deliberately simplistic -- "better than nothing" in both senses. For example, while it does have a limited capability to transliterate Chinese characters, this is entirely context-insensitive -- so if you feed it Japanese text then you get gibberish out.

The advantage of this simplistic nature is that it's pretty trivial to implement. You just have a big table of Unicode characters and their corresponding ASCII "equivalents". You could pull this straight from the Perl (or Ruby) source code if you decide to implement this functionality yourself.

I'm using something like this in my blog.

public class Post { public string Subject { get; set; } public string ResolveSubjectForUrl() { return Regex.Replace(Regex.Replace(this.Subject.ToLower(), "[^\\w]", "-"), "[-]{2,}", "-"); } }