Among them W3C Markup Validation Service:-
For completion of the developments, developers and the designers simultaneously need to validate the markups. There is always need to check the syntax of Web documents, written in formats such as HTML, XHTML etc. To resolve the problem of validation there are many a validation software but the one developed by W3C is the best. This Validator shows the coding problems clearly. The HTML documents are tested against defined syntax of HTML and marks all the discrepancies. The developers comparatively save time than using other such software services.