The Clarity keyboard is past of SwiftKey’s “Greenhouse” endeavor which is basically an experimental arm of the company where they take on projects that may or may not actually be released to the masses in the future. Clarity would be the first of its many experiments and what the keyboard tries to do is take into context what you’re trying to say before correcting it.
For example typing, “I will do this on the future,” would autocorrected to, “I will do this in the future,” which is correct. Normal keyboards might ignore the first sentence as there are no typos, but with Clarity it will detect that there is a grammatical mistake and will fix it for you. Users who are either trying to type that way on purpose or if there is slang involved can just press backspace to revert back to the original text.
So far it seems that this is the extent of Clarity and if you’d like to learn more about the keyboard and take it for a spin, which is currently in beta by the way, then head on over to SwiftKey’s Greenhouse page for the details.