| kkf | Uncompressed opening book files |
| kbz | Compressed opening book files |
| kln | Learned files |
| fkg | Fully solved EGTB files |
| fgz | Compressed fully solved EGTB files |
| peg | Partially solved EGTB files - used to recover from an interruption |
| idx | Opening book index file ("OpeningBook.idx") |
| idz | Compressed opening book index file ("OpeningBook.idz") |
| cfg | Engine configuration file ("KKFChess.cfg") |
| pgn | Portable Game Notation files |
| fen | FEN files. |
| tmp | Temporary files - can be removed |
| dat | Various data files |