REG (Windows Registry file)
Also known as: .reg file, registry file, registry export
A REG file (.reg) is a Windows Registry export — a text file containing registry keys and values. Double-clicking one merges those settings into the Windows Registry, which makes .reg files powerful but risky: a bad one can change critical system settings.
- A plain-text export of Windows Registry keys
- Double-clicking merges settings into the Registry
- Risky to run from untrusted sources — can break Windows
What a .reg file does
The Windows Registry is the central database of system and app settings. A .reg file is a snapshot of part of it, written as plain text. You can create one by exporting from the Registry Editor, and apply one by double-clicking it, which merges its keys back into the Registry.
This is how settings tweaks and fixes are commonly shared online — a single .reg file can flip a setting that would otherwise take many manual steps.
Why .reg files are risky
Merging a .reg file edits the Registry directly, with no undo prompt. A file from an untrusted source can disable security features, break apps, or destabilize Windows. Only run .reg files you understand or trust, and consider exporting a backup first.
The file itself is small plain text and harmless to keep on disk — the risk is in running it, not storing it. A System Restore point is a good precaution before applying registry changes.