Check if a URL is a valid Feed

From .NET 3.5 you can do this below. It will throw an exception if it's not a valid feed.

using System.Diagnostics;
using System.ServiceModel.Syndication;
using System.Xml;

public bool TryParseFeed(string url)
{
    try
    {
        SyndicationFeed feed = SyndicationFeed.Load(XmlReader.Create(url));

        foreach (SyndicationItem item in feed.Items)
        {
            Debug.Print(item.Title.Text);
        }
        return true;
    }
    catch (Exception)
    {
        return false;
    }
}

Or you can try parsing the document by your own:

string xml = "<?xml version=\"1.0\" encoding=\"utf-8\" ?>\n<event>This is a Test</event>";
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.LoadXml(xml);

Then try checking the root element. It should be the feed element and have "http://www.w3.org/2005/Atom" namespace:

<feed xmlns="http://www.w3.org/2005/Atom" xmlns:creativeCommons="http://backend.userland.com/creativeCommonsRssModule" xmlns:re="http://purl.org/atompub/rank/1.0">

References: http://msdn.microsoft.com/en-us/library/system.servicemodel.syndication.syndicationfeed.aspx http://dotnet.dzone.com/articles/systemservicemodelsyndication

you can use Feed Validation Service. It has SOAP API.