Why?
Startups can't afford recruiters, and recruiting without a recruiter sucks because you don't have a barrier between engineering and unserious applicants. FizzBuzz.md is that barrier.
Instead of making engineers sift through hundreds of resumes, kick off your hiring process with a challenge. If an applicant can't solve your code challenge, you don't need to see their resume.
Instead of addressing ambiguity in your challenge prompt with a live meeting, applicants can submit questions via a POST request to the FizzBuzz.md challenge API. If an applicant can't figure out how to send a POST request and render the challenge by setting a cookie via their browser devtools, their question was going to be a waste of time.
Other coding interview platforms constrain the scope of your challenge to a single file that needs to be solved in a bad web IDE. With these platforms, it's hard to see how applicants think about testing and architecture. Plus, taking a way a vimmer's vim or an emacer's emacs is cruel and unusual. With FizzBuzz.md, let your applicants use whatever editor they want and submit a link to their solution via POST request.