.tmp · application/octet-stream
What is a .tmp file?
Temporary File
About the format
A .tmp file is scratch space: a program needed somewhere to park data mid-operation — a download in progress, a document being saved (the write-to-temp-then-rename pattern that makes saves atomic), an installer unpacking itself — and named it .tmp, usually with a random name, usually in C:\Users\you\AppData\Local\Temp or C:\Windows\Temp. Well-behaved programs delete their temp files afterwards; crashed or lazy ones don't, which is how Temp folders quietly accumulate gigabytes. Cleanup is legitimate and built in: Settings → System → Storage → Temporary files, or Disk Cleanup, or (the classic) closing your programs and clearing %TEMP% by hand — a file that's genuinely in use will refuse deletion, which is your safety net. Two caveats: don't excavate Temp folders hunting for lost documents until you've checked the application's own recovery (Office keeps its own AutoRecover files), and a .tmp file's CONTENT is unknowable from the name — it's whatever its creator was doing, occasionally including sensitive data, which is an argument for letting cleanup tools purge them regularly.
How to open a .tmp file
Windows
- usually not opened — cleaned up (Settings → Storage → Temporary files)
- a hex viewer or file identifier if you must know what one is
macOS
- n/a
Linux
- n/a
Is a .tmp file dangerous?
No — inert leftovers. Safe to clean with the built-in tools.
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