The Markup Validator is a free service by W3C that helps check the validity of Web documents. It checks the syntax of Web documents, written in formats such as (X)HTML. The API uses SOAP protocol and responses are formatted in XML.
The following is a list of SDKs from our SDK directory that matched your search term. Though your definition of an SDK may differ, in our world, we define SDKs as platform- specific tools for consuming existing APIs of the sort we list in our API directory. For example, the Ruby SDK for consuming the Twitter Ads API. If you think an SDK, API, or other asset is missing from our directory, be sure to check our guidelines for making contributions to ProgrammableWeb.