The Science Page uses and recommends the following online HTML and CSS Validators and Link Checkers:
Ask - Search engine owned by InterActive Corp. and promoted across their suite of web properties. To a large degree they syndicate results and ads from Google.
Baidu - A leading Chinese search engine founded on January 1, 2000 by Robin Li and Eric Xu.
Bing - the default search in Windows. Has around 10% market share in the US.
Cliqz - a privacy-focused search engine and web browser
DuckDuckGo - privacy focused search engine founded by Gabriel Weinberg on February 29, 2008
Ecosia - search engine which uses profits from web search to plant millions of trees. They syndicate their core organic search results from Microsoft's Bing.
Gigablast - independent search engine created by Matt Wells in 2000
Google - the search engine with the largest reach. Larry Page and Sergey Brin founded the company on September 4, 1998. They are the default search engine in Chrome web browsers and most web browsers on Android phones. In addition they pay Apple to be the default search provider in Safari and Mozilla to be the default search provider in Firefox.