sitecheck
Modular web site spider for web developers.
More than just a link checker, sitecheck is a website spider (also known as a crawler) which can assist with SEO by testing an entire site plus both inbound links from search engines and outbound links to other sites for the following issues: looping redirects (HTTP 301/302), broken links (HTTP 404), server errors (HTTP 500), spelling mistakes, low readability scores (using the Flesch Reading Ease test), missing/empty/duplicate meta tags, duplicate content, slow page speed, W3C validation...