Moonlighting from his job as a programmer at Intel, he started a basic, open-source database using about 250 of his own records — the first entry was for a double 12-inch single by the Swedish D.J. the Persuader — and revealed it to fellow collectors in October 2000. Two years later, he took a buyout from Intel and devoted himself to Discogs.

The site, once run from a computer in Mr. Lewandowski’s closet and originally restricted to electronic music, has grown rapidly. It now has 37 employees around the world, 20 million online visitors a month and three million registered users. It eventually opened to all genres of music and has a mission of cataloging every record in existence.

The site’s supporters, including the more than 260,000 people who have contributed content, pursue that mission with zeal, but they still have a long way to go. Competing collector sites, like 45worlds, have plenty of titles that are missing from Discogs, like a 78 r.p.m. acetate of the Beatles’ “Devil in Her Heart” from 1963. And proprietary databases like Gracenote, owned by Tribune Media, claim more titles over all.

Casual users may simply consult Discogs to check the text on old labels or to see whether a record was released in colored-vinyl variations. Those who sign up for accounts can also tag items as being part of their collections, as well as communicate with other users and buy or sell copies. The most dedicated create and edit listings, actions for which there are strict and elaborate guidelines. The first rule: “You must have the exact release in your possession.” A 40,000-word post lays out how to identify run-out information — the obscure codes marked on the inner portion of a record, closest to the label.

“We are trying to approach it from a very factual point of view,” said Nik Kinloch, the first employee hired by Mr. Lewandowski. “You have the music release in front of you. What does it say on it? That is the source of truth for building the discography.”

Like Wikipedia, Discogs has sometimes heard from people or companies that want to remove unflattering information. But with Discogs, those requests tend to be more about D.J.s wanting to update old stage names than about the right to be forgotten.