What is the BLOB file format?
Steam client registry files are saved with the .blob extension, the primary example being ClientRegistry.blob. BLOB stands for Binary Large Object - a term for binary data stored as a single unit. Steam's .blob files are proprietary binary caches, not encrypted, that store client settings, login state, and app install records the Steam client validates at startup. Sometimes these files become corrupted and can cause Steam not to work properly.
ClientRegistry.blob is located in the Steam installation folder. On Windows, the default path is C:\Program Files (x86)\Steam. On macOS, the file is typically found under /Users/<username>/Library/Application Support/Steam. On Linux, the usual location is ~/.steam/steam.
The most practical reason to interact with this file is troubleshooting. Quitting Steam first, then deleting or renaming ClientRegistry.blob, is a long-standing fix when Steam fails to launch or update. Steam will create a new ClientRegistry.blob upon restarting that contains default settings. A related file, appupdatestats.blob, stores Steam update data and rarely causes the same problems.
Note that the generic .blob extension is also used by many unrelated programs - databases, firmware images, and game asset bundles - so confirm the file's source before acting. In modern Steam clients, ClientRegistry.blob has been largely superseded by VDF and ACF configuration files and may persist mainly as a legacy artifact.
Security & safety
RISK: LOWClientRegistry.blob is a local Steam cache, not an executable, so the file itself poses no risk and deleting it is safe (Steam rebuilds it; your games and account are stored elsewhere). The realistic cautions: only delete the file from your genuine Steam installation while Steam is fully closed; and because '.blob' is a generic extension, never assume an unknown .blob is harmless data - a .blob from an untrusted source could be a firmware image, packed payload or database dump, so identify its origin and scan downloads. Avoid 'blob viewer/opener' download sites, which are typically adware lures.
Format details
in a nutshell- Binary Large OBject (generic database/programming blob) - Generically, a .blob holds arbitrary binary data - a database BLOB column dump, a packed asset, or raw bytes from an application; meaning depends entirely on the producing program.
- Firmware / device image blob - Embedded and mobile workflows ship firmware or partition images as .blob files flashed to a device with vendor tools.
- Minecraft / game asset or cache blob - Some games and engines store packed assets or cache data in .blob files used only by that title.
Programs that open BLOB files
Windows1 app
Steam
Free There's nothing to open - Steam uses ClientRegistry.blob internally. To fix Steam problems: fully exit Steam, delete/rename ClientRegistry.blob in the Steam folder, relaunch (Steam rebuilds it). 
macOS1 app
Steam
Free Same as Windows: quit Steam, remove ClientRegistry.blob from the Steam application support folder, relaunch to rebuild it. It's a cache, not a document. 
Linux1 app
Steam
Free Quit Steam, delete ClientRegistry.blob from the Steam directory (~/.steam / ~/.local/share/Steam), relaunch; Steam regenerates it. Technical details
deep spec| Developer | Valve Corporation |
| Encoding | Binary (proprietary Valve format) |
| Byte order | Little-endian |
| Internal structure | Binary key-value cache storing account/login state, app install records, and depot configuration |
| Encryption | None - stored as unencrypted binary |
| Typical file size | Tens of KB to ~150 MB, depending on account history and cache state |
| Fixed filename | ClientRegistry.blob (also appupdatestats.blob for update data) |
| Supported OS | Windows, macOS, Linux |
| MIME type | application/octet-stream |
| File identification | By fixed filename in the Steam installation folder; no constant magic-byte signature documented |
| Integrity validation | Steam client validates internally; a corrupt or missing file is discarded and rebuilt on next launch |
| Format versioning | Undocumented Valve internal version; changes silently with Steam client updates |
| Current status | Largely deprecated - modern Steam clients rely on VDF and ACF files; .blob persists mainly as a legacy cache artifact |
| Windows default path | C:\Program Files (x86)\Steam\ClientRegistry.blob |
| macOS default path | /Users/<username>/Library/Application Support/Steam/ClientRegistry.blob |
| Released | 2003-2004 (with the Steam client) |
| Latest version | N/A (internal Steam client cache; no public versioned spec) |
| Specification | store.steampowered.com |
BLOB conversions
Community Q&A
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