Massive open online courses (MOOCs), one of the latest internet revolutions have engendered hope that constant iterative improvement and economies of scale may cure the “cost disease” of higher education. While scalable in many ways, providing feedback for homework submissions (particularly open-ended ones) remains a challenge in the online classroom. In courses where the student-teacher ratio can be ten thousand to one or worse, it is impossible for instructors to personally give feedback to students or to understand the multitude of student approaches and pitfalls. Organizing and making sense of massive collections of homework solutions is thus a critical web problem. Despite the challenges, the dense solution space sampling in highly structured home- works for some MOOCs suggests an elegant solution to providing quality feedback to students on a massive scale. We outline a method for decomposing online homework submissions into a vocabulary of “code phrases”, and based on this vocabulary, we architect a queryable index that al- lows for fast searches into the massive dataset of student homework submissions. To demonstrate the utility of our homework search engine we index over a million code sub- missions from users worldwide in Stanford’s Machine Learning MOOC and (a) semi-automatically learn shared structure amongst homework submissions and (b) generate specific feedback for student mistakes. Codewebs is a tool that leverages the redundancy of densely sampled, highly structured homeworks in order to force- multiply teacher effort. Giving articulate, instant feedback is a crucial component of the online learning process and thus by building a homework search engine we hope to take a step towards higher quality free education.