[NTG-context] testing for broken links to external documents

Dear all, is there a simple TeX/ConTeXt way to test in a TeX file whether a link to an external document is broken so that I get an error message if not? I am using numerous links to external files (on my hard drive) and I'd like to make sure that none of the links are broken without going manually trough them. Though not an issue at this point, and probably more complicated: Can one also check for broken links to web pages? I don't even know whether that's possible in Acrobat or whether there are tools out there that do that. Thanks, Matthias