Validator

Validation service: Markup

1. W3C Markup Validation Service(Html, Xhtml) 網頁標記語法驗證
2. Free Online HTML Validator - FreeFormatter.com
3. W3C CSS Validation Service
4. XML Validator offered by W3Schools
5. Accessibility validator: HiSoftware Cynthia Says Portal validate Section 508, WAI (?) / WCAG (?)

Linked data / Rich snippets

1. Bing 標記驗證程式
2. Google Structured Data Testing Tool: Rich snippets

other

1. jsFiddle using jsLint[Last visited: 2012-04-21]
2. Link Checker
3. RSS validator[1] for Atom and RSS