Using the API for the W3C HTML Validator

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The W3C has introduced an API for their HTML Validator.

It is not a SOAP web service, but it does return XML that can be parsed, so now you have the ability to incorporate validation to any web application, Windows program or wherever you want. It works just as the normal validator, by specifying a URL, but you have to add the “output=soap12″ parameter to the URL like so: http://validator.w3.org/check?uri=http://www.google.com&output=soap12.

I’ve been playing a little with the possibilities and created a class that encapsulates the validation process and wraps the results up in a suitable class.

The collection of errors and warnings can be bound directly to a GridView or Repeater without additional code.

This gives you a very easy, but powerful way of dealing with the validator.

Examples of use

Even thought the class is very small and its functionality limited, it still gives you all the relevant information from the validation.

Here’s an example of some of the possibilities of the class.

using (HtmlValidator val = new HtmlValidator("http://www.google.com"))


   if (!val.Validate())


     grid.DataSource = val.Errors; // or val.Warnings


     lbDoctype.Text = val.Doctype;

     lbCharset.Text = val.Charset.BodyName;

     foreach (HtmlValidator.ValidationError error in val.Errors)


     DoSomething(error.Message, error.LineNumber, error.ColumnIndex);




Download HtmlValidator.cs below and add it to any C# project. If you want to use it in an ASP.NET project, just put it in the App_Code folder.


HtmlValidator.zip (1,43 KB)


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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.


Using the API for the W3C HTML Validator
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  • Vasanth

    Dear Sir ,

    While i am downloading HtmlValidator.zip , the page showing config error. can you please help me and send the file.

    Thanks & Regards,

  • http://thecornercoffeetable.blogspot.com/ Karthik


    the link to download the HtmlValidator.zip on this post seems to be broken. Could you please mend the same?
    Am sure this utility of yours would be a pretty useful one for all.


  • Cip

    Yep, the download link is still broker. :(

  • http://geekswithblogs.net/mnf/Default.aspx Michael Freidgeim

    Link to API http://www.madskristensen.dk/blog/ct.ashx?id=81e2e894-ad13-4559-9c69-695d54dce1ee&url=http%3a%2f%2fvalidator.w3.org%2fdocs%2fapi.html -not working

  • http://geekswithblogs.net/mnf/Default.aspx Michael Freidgeim

    And Download is not available as well

  • http://forum.joltiy.ru/member.php?u=34603 themusclemaximizer

    Good write-up, I’m regular visitor of one’s site, maintain up the excellent operate, and It is going to be a regular visitor for a lengthy time.

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