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Yaz0 is a data compression algorithm used in many Nintendo games.



All values in the header are big endian even on Switch.

Offset Type Description
0x0 char[4] Magic ("Yaz0")
0x4 u32 Uncompressed data size
0x8 u32 Data alignment (archive must be loaded into a N-byte aligned buffer)
0xc u32 Unused


The algorithm is documented on the MK8 wiki

Usage in Breath of the Wild

Yaz0 is the only compression algorithm that is used in Breath of the Wild. Many resources, such as bactorpacks and BYMLs, are compressed. However, content files that are inside of archives that have already been compressed (such as ActorParam files) are typically uncompressed.

Extensions that start with an s indicate that the file is compressed using the Yaz0 format. For consistency reasons and to reduce visual noise, ZeldaMods chooses to omit the prefix when referring to file extensions.