How do I see what's inside a .reg file without running it?

Drop it here, or on Windows right-click it and choose Edit (or open it in Notepad). Notepad shows the raw lines, with long values as rows of hex numbers; this page decodes those and tells you what the risky keys do.

Is it safe to run a .reg file from the internet?

Only if you trust the source and know what it changes. A .reg file cannot carry a program, but it can make one start every time Windows does, point a setting at a file elsewhere, or switch off protections. Check the flagged keys here first.

How do I undo a .reg file I already ran?

There is no automatic undo. If you exported the same keys before importing, import that backup; otherwise use System Restore, or change the values back by hand in Registry Editor using the list on this page.

Can it open registry hives like NTUSER.DAT?

No. Hive files are the registry's own binary database, not .reg text. This page reads .reg files from Registry Editor in both its formats: Version 5.00 and the older REGEDIT4.

Stays on your computer How this works

Open a REG file: see what it would change before you run it

A .reg file changes the Windows registry the moment it is double-clicked. Drop one here to read every key and value it would write or delete, in plain words, with changes to startup programs and security settings flagged. Nothing is changed, and the file is not uploaded.

Drop a .reg file here, or click to choose oneIt is opened by your browser, on this computer. Nothing is uploaded.

About registry files

The Windows registry holds the settings of Windows and most programs. Registry Editor can save part of it as a .reg file, and double-clicking a .reg file - after one "Are you sure?" - writes everything in it back. That is how tweaks, fixes and settings get shared: "download this .reg file to turn off X". It is also a way to make a program start with Windows, switch off parts of Microsoft Defender, or take over what happens when you open a file type, all in one double-click.

This page reads the file without importing it. It lists each key, who it applies to (you, or every user of the computer), and each value decoded - text, numbers, lists and paths rather than rows of hex - and marks the keys that matter: startup entries, Winlogon, Image File Execution Options, Defender, services, policies, file-type commands and more. It is free to use, with no account and no upload limit, and it runs entirely in your browser: nothing is uploaded, and while the page stays open, a feature you have already used keeps working offline.

What you can do

Read a .reg file on Windows without risk of importing it, or on a Mac, Linux or phone
See every key added or deleted, and every value set or removed
Read values decoded: DWORD and QWORD numbers in decimal and hex, expandable strings, multi-string lists, binary as hex
Get flags for changes to startup programs, sign-in, Defender, UAC, services and file associations
Search large exports and show only the flagged keys

How to check a .reg file

Drop the .reg file on the box above, or click the box and choose it. Do not double-click it first.
Read the summary and any keys marked in red.
If everything matches what you expected the file to do, import it on Windows. If not, delete it.

Questions

How do I see what's inside a .reg file without running it?: Drop it here, or on Windows right-click it and choose Edit (or open it in Notepad). Notepad shows the raw lines, with long values as rows of hex numbers; this page decodes those and tells you what the risky keys do.
Is it safe to run a .reg file from the internet?: Only if you trust the source and know what it changes. A .reg file cannot carry a program, but it can make one start every time Windows does, point a setting at a file elsewhere, or switch off protections. Check the flagged keys here first.
How do I undo a .reg file I already ran?: There is no automatic undo. If you exported the same keys before importing, import that backup; otherwise use System Restore, or change the values back by hand in Registry Editor using the list on this page.
Can it open registry hives like NTUSER.DAT?: No. Hive files are the registry's own binary database, not .reg text. This page reads .reg files from Registry Editor in both its formats: Version 5.00 and the older REGEDIT4.

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