What is the BACKUP file format?
The .backup extension is used by ISAPI Loader - a utility for Internet Information Services (IIS) administrators that enables updating ISAPI applications and .dll libraries without restarting IIS servers - as well as by many other programs and operating systems.
A .backup file contains a copy of another file kept as a fallback; it is not a distinct format. Its actual content type is whatever the original file was - an XML config, a ZIP archive, an SQLite database, a disk image, or plain text - and it carries no identifying magic bytes of its own.
.backup data generated by ISAPI Loader and similar tools is saved automatically. A .backup file is used to restore main files to a previous state in case of file loss or other failure. Often the simplest approach is the rename-back trick: remove the .backup suffix, restore the real extension, and open the file in the appropriate program.
Security & safety
RISK: LOWA .backup is just a copy, so it's only as risky as whatever it duplicates - a backup of a clean config is harmless; a backup of a malicious file carries the same risk as the original. Don't blindly delete a .backup until you've confirmed the live data is intact: it may be your only recovery copy. When opening one of unknown origin, check its real type before acting, and never rename a mystery .backup to .exe/.dll and run it. App/device backups can also contain sensitive data (saved passwords, tokens, personal data), so store and share them carefully.
Format details
in a nutshell- App-specific backup exports - Many apps name their export with .backup (firewall/router configs, MoneyWiz, password managers, IoT/firmware), each readable only by that same app.
Programs that open BACKUP files
Windows5 apps
7-Zip
Open-source Inspect an unknown .backup: try opening it as an archive, or check its first bytes to identify the real underlying format. 
NotePad++ text editor
Open-source If the original was text/config (XML/JSON/INI), open the .backup directly to read or copy out its contents. 
Originating app/device (Restore/Import)
Built-in The reliable path: open the program or device web UI that made the .backup and use its Restore/Import function to load it back.
Rename-back trick
Built-in Copy the .backup, rename the copy's extension to the original (.sqlite/.xml/.json/.zip…), then open it in the matching program.
DB Browser for SQLite
Open-source If the header reads 'SQLite format 3', open the .backup in DB Browser for SQLite to read the data. 
macOS2 apps
Originating app (Restore/Import)
Built-in Use the app's own Restore/Import to load the .backup; for files, duplicate and rename the extension back to the original type.
file + a text editor / The Unarchiver
Built-in Run file name.backup in Terminal to detect the real type, then open with the matching tool (editor, archiver, DB viewer). 
Linux1 app
file + matching tool
Built-in Run file something.backup to identify the type, then cp it to the right extension and open with the appropriate program. Technical details
deep spec| File role | Fallback copy - not a distinct format; a duplicate of the original file with `.backup` appended to preserve it as a spare |
| Content type | Inherits from the original: may be XML, JSON, plain text, SQLite data, a ZIP-based archive, a disk image, or any binary |
| Magic bytes | None specific to `.backup` - the leading bytes mirror the original file's format (e.g. `53 51 4C 69 74 65` for an SQLite source) |
| MIME type | `application/octet-stream` (generic binary default) |
| Naming convention | Original filename with `.backup` appended - e.g. `config.xml.backup`, `database.db.backup`, or `Settings.backup` |
| Common sources | ISAPI Loader (IIS), database engines, macOS system tools, iOS device managers, backup agents, and custom scripts |
| Creation trigger | Automatic pre-update snapshot before a file is replaced, or an explicit export/backup action inside the originating app |
| Recovery method | Use the originating app's restore or import function, or the rename-back trick: strip the `.backup` suffix, restore the original extension, reopen |
| Platform support | Cross-platform - generated and consumed on Windows, macOS, Linux, iOS, and Android |
| Type detection | `file something.backup` on Linux or macOS reveals the underlying format; hex editor inspection works on any OS |
| Compression | Possible if the original was compressed; `.backup` itself adds no compression layer |
| Encryption | Possible when the originating app encrypts its backups (e.g. encrypted iOS device backups); otherwise plain binary |
| Related extensions | `.bak`, `.sav`, `.old`, `.abf` - all serve the same fallback-copy role by informal convention |
| ISAPI Loader use | Saves `.backup` copies of ISAPI `.dll` and application files so IIS can be updated hot, without a server restart |
| Released | Long-standing convention (same idea as .bak), used across many apps |
BACKUP conversions
Community Q&A
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Frequently asked questions
How do I open a .backup file?
What program opens a .backup file?
Can I delete .backup files?
How do I find out what's inside a .backup file?
file name.backup on macOS/Linux. The header tells you the real type and which tool to use.
