What is the LRLIBRARY file format?
An .lrlibrary file is the local library used by the cloud-based version of Adobe Lightroom, the desktop app Adobe now ships simply as Lightroom (formerly Lightroom CC), separate from Lightroom Classic. It arrived with the cloud Lightroom ecosystem in 2017.
Despite the extension, it is not a single file. On macOS it is a package; on Windows it is an ordinary folder. Lightroom creates it automatically at install and names it Lightroom Library.lrlibrary inside your Pictures folder. Inside sits a subfolder with a long alphanumeric name holding an originals folder of imported photos in dated sub-folders, one or more .mcat catalog files, helper databases, a cache, and migration and edit logs. The catalog databases are SQLite.
Because this Lightroom keeps your photos in the cloud, the .lrlibrary works mainly as a local cache and working store rather than the master record. That is the main difference from Lightroom Classic's .lrcat catalog, which is the primary database.
Security & safety
RISK: LOWThe .lrlibrary is a local data package created by Adobe Lightroom and carries no executable code, so it is not a malware vector by itself. The main practical risk is disk usage, since it can grow to many gigabytes as originals are cached locally. Deleting it is safe only if your photos are fully synced to Adobe's cloud or if you no longer use the cloud-based Lightroom; deleting it while unsynced originals remain can lose those images.
Format details
in a nutshellPrograms that open LRLIBRARY files
Windows2 apps
Adobe Lightroom
Paid Install and launch Adobe Lightroom (the cloud-based, non-Classic app); it automatically loads the Lightroom Library.lrlibrary from your Pictures folder on startup.
Windows File Explorer
Built-in Open the Lightroom Library.lrlibrary folder to inspect the 'originals' sub-folders and catalog files, though it will not render the library as a photo collection. 
macOS2 apps
Adobe Lightroom
Paid Install and open Adobe Lightroom (cloud-based); it reads the Lightroom Library.lrlibrary package automatically and displays your synced photos.
Finder (Show Package Contents)
Built-in Right-click the .lrlibrary package and choose Show Package Contents to browse the originals folder, .mcat catalog and log files inside. Technical details
deep spec| Encoding | Binary; container is a folder/package holding SQLite databases plus copied image originals |
| Container | macOS package (Finder bundle) on Mac; ordinary folder on Windows |
| Structure | The .lrlibrary is a bundle rather than one file. Inside is a randomly-named subfolder (a long alphanumeric identity string) that holds an 'originals' folder with imported photos stored in dated sub-folders, one or more .mcat catalog files, a helper/preview cache, migration and edit logs, and a folder for temporary edits. |
| Compression | Cached originals are stored in their native format (uncompressed by the container); preview and cache data may be compressed internally |
| Integrity | Relies on the SQLite databases' internal page structure; cloud sync reconciles integrity against Adobe's servers |
| Typical size | Ranges from a few hundred MB to well over 100 GB depending on how many originals are stored locally |
| Platforms | Windows, macOS |
| Notes | This is the local library for the cloud-based Adobe Lightroom desktop app (the non-Classic version), not Lightroom Classic. It acts as a local cache of cloud-hosted data rather than the primary store, so it can be regenerated after a fresh sync. It is created automatically at install and named 'Lightroom Library.lrlibrary' in the user's Pictures folder by default. |
| Byte order | Little-endian (inherited from the SQLite databases inside) |
| Released | 2017 |
LRLIBRARY conversions
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