What is the NSZ file format?
.nsz is a Compressed Nintendo Switch Package - a community-created lossless compressed variant of the .NSP game package format used on the Nintendo Switch. Introduced in 2019 by developer nicoboss via the open-source NSZ tool, it is not an official Nintendo format but is widely adopted in the homebrew and emulation community.
Structurally, an .nsz file is a PFS0 partition container (the same underlying format as .nsp) in which each NCA (Nintendo Content Archive) payload has been recompressed as an .ncz file using the Zstandard (zstd) lossless algorithm. The first 0x4000 bytes of each .ncz entry are preserved intact from the original encrypted NCA header, followed by a block-compressed payload section. The file carries a PFS0 magic signature (50 46 53 30) at byte offset 0, identical to a standard .nsp.
Compression typically achieves a 40-80% size reduction while remaining fully lossless: decompressing an .nsz reproduces the original .nsp byte-for-byte. SHA-256 integrity hashes embedded in the CNMT metadata NCA verify correctness after decompression. The .nsz format mirrors the relationship between .XCZ and .XCI - both pairs cover compressed versus uncompressed Switch game images from package and cartridge sources respectively.
Modern Ryujinx-family emulators can load .nsz files directly without a prior decompression step. The nsz command-line tool and GUI utilities such as NSC_BUILDER support both compression and decompression on Windows, Linux, and macOS.
Security & safety
RISK: MEDIUMThe NSZ format itself is data, not executable code, so the file won't 'run' on your PC. The real issues are legal and operational: using NSZ requires console encryption keys (prod.keys) and the games inside are copyrighted - compressing your own legally-dumped games is the only defensible use, while downloading or sharing others' Switch games is piracy. Practically, get the NSZ tool only from its official GitHub (nicoboss/nsz); 'NSZ converter/opener' sites and bundled installers are common malware/adware bait in this scene. Running pirated content on a real Switch also risks a Nintendo console ban.
Format details
in a nutshell- NVIDIA nTune benchmark file (legacy) - Old benchmark/profile data from NVIDIA's discontinued nTune overclocking tool (the original db_name).
- Nullsoft / generic compressed data (rare) - Occasionally seen as a generic 'compressed' marker by unrelated tools.
Programs that open NSZ files
Windows3 apps
NSZ (decompress tool)
Open-source Run 'nsz -D game.nsz' to decompress back to the original .nsp, or use the bundled GUI. The reference tool for the format.
Ryujinx-family emulator
Open-source Add the game directory; modern Ryujinx builds load .nsz directly (requires your own prod.keys / firmware).
NSC_BUILDER / NSCB
Open-source GUI toolkit that compresses/decompresses and inspects NSP/NSZ/XCI/XCZ; convenient for batch work. 
macOS1 app
NSZ (decompress tool)
Open-source Python tool runs on macOS too: 'nsz -D game.nsz'. Ryujinx-family builds for macOS can load NSZ directly. 
Linux2 apps
NSZ (decompress tool)
Open-source pip install nsz, then 'nsz -D game.nsz' to restore the .nsp, or '-C' to compress an .nsp.
Ryujinx-family emulator
Open-source Load the .nsz directly in the emulator (needs your own keys/firmware). Technical details
deep spec| Container format | PFS0 partition filesystem - identical header structure to .nsp |
| File signature (magic bytes) | PFS0 (0x50 0x46 0x53 0x30) at byte offset 0 |
| Byte order | Little-endian |
| Internal payload type | NCA files replaced by .ncz entries (Zstandard-compressed NCA) |
| NCZ header preservation | First 0x4000 bytes of each .ncz entry retain the original encrypted NCA header unchanged |
| Compression algorithm | Zstandard (zstd) - lossless |
| Typical compression ratio | 40-80% size reduction versus the original .nsp, depending on game content type |
| Block-mode compression | Newer .ncz entries use block-based Zstandard for random-access decompression without a full decode pass |
| Integrity verification | SHA-256 hashes in the CNMT metadata NCA verify each NCA payload after decompression |
| Encryption model | NCA content is decrypted before Zstandard recompression; the title key and cert ticket are retained in the container |
| Typical file size | 200 MB - 15 GB compressed (large titles remain multi-GB even after compression) |
| MIME type | application/octet-stream |
| Lossless round-trip | Decompressing an .nsz reproduces the source .nsp bit-for-bit |
| Native emulator support | Ryujinx-family emulators parse .nsz directly without requiring prior decompression |
| Format origin | Community format created by nicoboss; not an official Nintendo format |
| Released | 2019 (NSZ tool by nicoboss) |
| Latest version | Tracks the NSZ tool releases (actively maintained on GitHub) |
| Open standard | Yes · royalty-free |
| Specification | github.com |
NSZ conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about NSZ files.
