Online Places to Find External, Internal, nofollow Links on Web Page
For on page Search Engine Optimization (SEO), it is important to keep track of external links and see whether they are dofollow or nofollow. In fact these things are important for PageRank building of the site as well. In webmaster tools, you can find number of backlinks that your site is getting, but then are you diverting your backlinks to some other place as well.
