The LCSH are the vocabulary libraries around the world use to describe what books are about, about half a million have been written and are maintained by LC since 1898. They give them away in bulk but only as linked data (JSON-LD and N-Triples). MARC format is what libraries actually use, LC sells them in bulk for convenience. Currently there was no way to get this data packaged cleanly openly and freely.

The mirror is here: https://bibliotecaalonsocossio.com/lcshmirror/

What’s there:

The full file every week: 58 MB gzipped MARC 21, 56 MB gzipped MARCXML (~570 MB uncompressed), plus a CSV list of every record (LCCN, last-change date, heading).

Change files per release: only the records new or changed since last week, plus a list of deleted headings. Compared by MARC content, not by dates.…