Known colloquially as the 'Cheka bags', because they were discovered stashed inside cloth bags, the KGB files are a document trove that was found during the 1991 barricades inside the KGB building in Rīga.
Those who wish to see the KGB documents will have to register, so they could be identified if they happen to violate data privacy regulations.
This year's publication of KGB files will be a virtual exhibition of KGB documents and explanatory notes. The published documents will include phone catalogs, a list of KGB employees, as well as a card index, that list outside collaborators.
The National Archives Management says most of the KGB documents to be published tomorrow are in Russian and handwritten.
Starting from May 1, 2019, also other KGB documents will be published.
Read more about the KGB archives here. A complementary piece discusses a couple of problems with the reliability of the files to be published.