Existing tools include:

• Script to interface with Zotero locally, uses MozRepl dependency in Zotero to inject Javascript over HTTP (this is because the JS needs to be run from within Zotoer). Most of the toolchains specified in the comments by the author have been archived, and not working for Zotero 5.0.
  • An alternative exists with the "Better Bibtex" project using a debug bridge that essentially does the same thing.
• pyzotero-local, archived in 2022. This one interfaces directly with the SQL database, but not recommended by Zotero.

However, access to the SQLite database should be done only in a read-only manner. Modifying the database while Zotero is running can easily result in a corrupted database. A caching layer breaks the normal file-locking in SQLite that allows for safe concurrent file access, and even if Zotero is shut down before accessing the file, modifying the database directly bypasses the data validation and referential integrity checks performed by Zotero and the Zotero web API that are required for Zotero to function properly. Generally, the SQLite database should be viewed as an internal database that has the benefit of being externally readable for people who want to get the data out in other ways. (src)

• Similar archived code pyzottk.