SAN FRANCISCO — Before the Internet, books were written — and published — blindly, hopefully. Sometimes they sold, usually they did not, but no one had a clue what readers did when they opened them up. Did they skip or skim? Slow down or speed up when the end was in sight? Linger over the sex scenes?

A wave of start-ups is using technology to answer these questions — and help writers give readers more of what they want. The companies get reading data from subscribers who, for a flat monthly fee, buy access to an array of titles, which they can read on a variety of devices. The idea is to do for books what Netflix did for movies and Spotify for music.

“Self-published writers are going to eat this up,” said Mark Coker, the chief executive of Smashwords, a large independent publisher. “Many seem to value their books more than their kids. They want anything that might help them reach more readers.”

Last week, Smashwords made a deal to put 225,000 books on Scribd, a digital library here that unveiled a reading subscription service in October. Many of Smashwords’ books are already on Oyster, a New York-based subscription start-up that also began in the fall.