How to validate that a string doesn’t contain HTML using C#

The following will match any matching set of tags. i.e. <b>this</b>

Regex tagRegex = new Regex(@"<\s*([^ >]+)[^>]*>.*?<\s*/\s*\1\s*>");

The following will match any single tag. i.e. <b> (it doesn’t have to be closed).

Regex tagRegex = new Regex(@"<[^>]+>");

You can then use it like so

bool hasTags = tagRegex.IsMatch(myString);