Validating a URL with Regular Expressions

I had to build web form that took user input from standard ASP.NET input controls. In one of the text boxes the user must enter a valid URL, so I had to make some validation logic.

But first of all, I had to find out what kind of URL’s we would accept as being valid. These are the rules we decided upon:

The protocol must be http or https

Sub domains are allowed

Query strings are allowed

Based on those rules, I wrote this regular expression:

(http|https)://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?

It is used in a RegularExpressionValidator control on the web form and on a business object in C#.

<asp:RegularExpressionValidator runat="Server"


   ControlToValidate="txtUrl" 
   ValidationExpression="(http|https)://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?"
   ErrorMessage="Please enter a valid URL"

Display="Dynamic" />

Here is the server-side validator method used by the business object:

using System.Text.RegularExpressions;


private bool IsUrlValid(string url)
{
   return Regex.IsMatch(url, @"(http|https)://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?");

}

You can add more protocols to the expression easily. Just add them to the beginning of the regular expression:

(http|https|ftp|mailto)://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?

You can also allow every thinkable protocol containing at least 3 characters by doing this:

([a-zA-Z]{3,})://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?

Comments

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Mads Kristensen currently works as a Senior Developer at Traceworks located
in Copenhagen, Denmark. Mads graduated from Copenhagen Technical Academy with a multimedia degree in
2003, but has been a professional developer since 2000. His main focus is on ASP.NET but is responsible for Winforms, Windows- and
web services in his daily work as well. A true .NET developer with great passion for the simple solution.

http://www.madskristensen.dk/

There are 4 Comments. Add Yours.

Guest
November 7, 2008 at 1:48 pm

this is a good article
Guest
January 22, 2009 at 5:36 am

this logic is not working for any illegal URL. It always returns true.
Guest
November 13, 2009 at 9:11 am

Comment: *
TheKiller
February 9, 2010 at 4:27 pm

here is my URL:

http://www.crazygirls.com.tw:8000/index.html

hope you can validate this. have a nice day