You can run it locally - that's the default way to use it. "pip3 install datasette", create your SQLite database file and run "datasette mydb.db" to start exploring.

I've run it successfully on SQLite files up to a GB in size and theoretically it should work with much bigger files than that.

The https://publish.datasettes.com/ tool works by taking your uploaded CSVs and running my "csvs-to-sqlite" script on them, then deploying the datasette application alongside that new SQLite database file.