Michael Hartl

Welcome to Michael Hartl’s home on the Web!

I’m a founder and principal author at Learn Enough, a tech education company that produces books, videos, and online courses on web development and related subjects, including the command line, text editors, version control, HTML, CSS & Layout, JavaScript, and Ruby.

Learn Enough is an outgrowth of the Ruby on Rails Tutorial, which has been the leading introduction to web development with Rails since its launch in 2010. Once called his “favorite book” by Wikipedia founder Jimmy Wales, the print edition of the Ruby on Rails Tutorial has garnered over 450 5-star reviews on Amazon. Like all the main Learn Enough tutorials, the Rails Tutorial is available as a book, video series, and self-paced online course.

I’m also (in)famous as the author of The Tau Manifesto, an influential math essay that argues that “pi is wrong”—the right number being $\tau\ \mathrm{(tau)} = C/r = 6.283185\ldots$ The Tau Manifesto’s introduction of $\tau$ as the “true circle constant” has had a significant impact on geek culture, including changing the time of day MIT announces its admissions decisions and being supported by the official Google calculator. Meanwhile, its associated holiday, Tau Day, is celebrated annually on 6/28 by thousands of math nerds around the world.

My educational background is in physics, with a bachelor’s degree from Harvard and a Ph.D. from Caltech, where I studied black hole dynamics and was an award-winning instructor in theoretical and computational physics. I’m also an alumnus of Y Combinator, the entrepreneur program that has produced companies such as Reddit, Stripe, Coinbase, Dropbox, and Airbnb.