Registry Preview - Microsoft PowerToys

Registry Preview is a standalone utility for viewing, editing, and understanding Windows Registry (.reg) files. Preview what changes will be made to your system before importing registry files.

Overview

Registry Preview provides:

Visual representation of .reg file contents
Syntax highlighting for registry data
Hex editor for binary values
Safety preview before applying changes
File comparison capabilities

Activation

Open Registry File

Double-click a .reg file or right-click and choose “Open with Registry Preview.”

Review Changes

Examine the registry keys, values, and data that will be modified.

Edit if Needed

Make changes to registry values directly in Registry Preview.

Apply or Save

Apply changes to registry or save as modified .reg file.

Registry Preview is a separate application from the PowerToys Settings. Launch it from Start Menu or by opening .reg files.

Interface

Main Window

From source /src/modules/registrypreview/RegistryPreview/RegistryPreviewXAML/MainWindow.xaml.cs:22-88:

public sealed partial class MainWindow : WindowEx
{
    private const string APPNAME = "RegistryPreview";
    
    private JsonObject jsonWindowPlacement;
    private string settingsFolder;
    private string windowPlacementFile = "app-placement.json";
    
    private RegistryPreviewMainPage MainPage { get; }
}

Features:

Custom title bar with theme support
Window position and size persistence
AppIcon: Assets\RegistryPreview\RegistryPreview.ico
Minimum size: 320x240 pixels

File Structure Display

Tree View
List View

Registry keys displayed in hierarchical tree:

HKEY_CURRENT_USER
└─ Software
   └─ Microsoft
      └─ Windows
         └─ CurrentVersion

Expandable/collapsible nodes
Visual hierarchy
Key path navigation

Name	Type	Data
(Default)	REG_SZ	(value not set)
EnableFeature	REG_DWORD	0x00000001 (1)
InstallPath	REG_SZ	C:\Program Files\App

Value Types

Registry Preview displays all registry value types:

Supported Types

REG_SZ: String value
REG_EXPAND_SZ: Expandable string (environment variables)
REG_MULTI_SZ: Multi-string value (array of strings)
REG_DWORD: 32-bit number
REG_QWORD: 64-bit number
REG_BINARY: Binary data
REG_NONE: No defined type

Features

Syntax Highlighting

Registry file syntax with color coding:

Registry keys (blue)
Value names (black)
Value types (green)
Data values (red)
Comments (gray)
Errors (red underline)

Hex Editor

Binary data editing with hex view: Implementation: /src/modules/registrypreview/RegistryPreviewUILib/Controls/HexBox/

Hex Editor Features

From source /src/modules/registrypreview/RegistryPreviewUILib/Controls/HexBox/AddressFormat.cs:

Hex and ASCII dual view
Byte-level editing
Address display formatting
Copy hex values
Search in binary data
Data type interpretation

Clipboard Integration

From source /src/modules/registrypreview/RegistryPreviewUILib/ClipboardHelper.cs:

Clipboard Operations

Copy registry keys
Copy values and data
Paste registry snippets
Export selections to clipboard

File Operations

Open

Open .reg files
Recent files list
Drag and drop support
Command-line arguments

Save

Save modifications
Save as new file
Export selected keys
Backup before apply

Import

Apply to registry
Preview before import
Undo support
Backup creation

Compare

Compare two .reg files
Highlight differences
Merge changes
Conflict resolution

Safety Features

Editing the Windows Registry can cause system instability if done incorrectly. Always review changes carefully and create backups.

Preview Before Apply

Open Registry File

Load .reg file in Registry Preview.

Review All Changes

Examine every key and value that will be modified.

Understand Impact

Research unfamiliar registry keys before applying.

Create Backup

Export current registry state for affected keys.

Apply Changes

Only after thorough review, apply changes.

Validation

File Validation

Registry Preview validates:

.reg file format correctness
Registry path syntax
Value type compatibility
Data format validity
Encoding (UTF-16 LE with BOM)

Invalid entries are highlighted before import.

Use Cases

Software Configuration

Review Application Settings:

Examine registry changes from installers
Understand what settings are modified
Customize application configurations
Export settings for backup

Example: Before installing software, open its .reg file to see what registry keys it modifies.

System Tweaking

Windows Customization:

Review registry tweaks from online sources
Understand what optimizations do
Test registry modifications safely
Create custom tweak collections

Example: Found a Windows 11 optimization .reg file online - preview it in Registry Preview to understand changes before applying.

Troubleshooting

Registry Issue Diagnosis:

Export and examine problematic registry keys
Compare working vs. broken configurations
Identify incorrect values
Create fix .reg files

Example: Application won’t start - export its registry keys, compare with working machine, identify differences.

Development & Testing

Developer Workflows:

Test registry changes for applications
Create installation registry scripts
Debug registry-related issues
Version control registry configurations

Example: Developing installer - create .reg files for default settings, preview and test before deployment.

Documentation

Registry Change Documentation:

Document what registry changes do
Create annotated .reg files
Share registry configurations
Provide visual guides

Example: Write documentation showing exact registry values changed by configuration tool.

Registry File Format

.REG File Structure

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\MyApp]
"Version"="1.0.0"
"InstallPath"="C:\\Program Files\\MyApp"
"Enabled"=dword:00000001
"Settings"=hex:01,00,00,00,0f,00,00,00

[HKEY_CURRENT_USER\Software\MyApp\Advanced]
"Features"=hex(7):46,00,65,00,61,00,74,00,75,00,72,00,65,00,31,00,00,00,\
  46,00,65,00,61,00,74,00,75,00,72,00,65,00,32,00,00,00,00,00

; Delete a key
[-HKEY_CURRENT_USER\Software\OldApp]

; Delete a value
[HKEY_CURRENT_USER\Software\MyApp]
"OldSetting"=-

Format Details

Header
Keys
Values
Comments

All .reg files must start with:

Windows Registry Editor Version 5.00

This identifies the file format (Windows 2000 and later).

Registry keys in square brackets:

[HKEY_LOCAL_MACHINE\Software\Company\Product]

To delete a key, prefix with minus:

[-HKEY_CURRENT_USER\Software\OldApp]

Value format: "Name"=type:dataString (REG_SZ):

"AppName"="My Application"

DWORD (32-bit):

"Version"=dword:00000001

QWORD (64-bit):

"LargeValue"=hex(b):01,00,00,00,00,00,00,00

Binary:

"Data"=hex:00,01,02,03,04,05

Multi-String (REG_MULTI_SZ):

"List"=hex(7):49,00,74,00,65,00,6d,00,31,00,00,00,49,00,74,00,65,00,\
  6d,00,32,00,00,00,00,00

To delete a value:

"OldValue"=-

Lines starting with semicolon are comments:

; This is a comment
; Comments are ignored when importing

Advanced Features

Window Placement Persistence

From source /src/modules/registrypreview/RegistryPreview/RegistryPreviewXAML/MainWindow.xaml.cs:38-81:

Window State Management

Registry Preview saves window position and size:

settingsFolder = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData) + 
                 @"\Microsoft\PowerToys\" + APPNAME;
windowPlacementFile = "app-placement.json";

Saved state:

Window position (X, Y)
Window size (Width, Height)
Validated before restore (minimum 320x240)
Per-user settings storage

Theme Support

Automatic theme detection and application:

Light mode
Dark mode
High contrast
Follows Windows theme

Title Bar Customization

From source /src/modules/registrypreview/RegistryPreview/RegistryPreviewXAML/MainWindow.xaml.cs:44-48:

// Extend canvas to include title bar for theming
ExtendsContentIntoTitleBar = true;
SetTitleBar(titleBar);
AppWindow.SetIcon("Assets\\RegistryPreview\\RegistryPreview.ico");

File Association

Registry Preview can be set as default .reg file handler:

Replaces default registry editor prompt
Previews before import
Safer than direct import

Configuration

Settings Location

Settings Storage

Registry Preview settings stored at:

%LOCALAPPDATA%\Microsoft\PowerToys\RegistryPreview\

Files:

app-placement.json - Window position and size
User preferences and recent files

Appearance Options

Font size for registry display
Color scheme (follow system or custom)
Hex editor display format
Tree view indentation

Editor Preferences

Auto-save enabled/disabled
Backup before apply
Confirmation dialogs
Default open/save location

Keyboard Shortcuts

Shortcut	Action
`Ctrl + O`	Open .reg file
`Ctrl + S`	Save changes
`Ctrl + Shift + S`	Save as
`Ctrl + F`	Find in file
`Ctrl + H`	Find and replace
`Ctrl + C`	Copy selected
`Ctrl + V`	Paste
`Ctrl + Z`	Undo
`Ctrl + Y`	Redo
`F5`	Refresh
`Ctrl + W`	Close file

Troubleshooting

Can't Open .reg Files

Issues:

File association not set
Registry Preview not in PATH
File encoding incorrect

Solutions:

Right-click .reg file > Open with > Registry Preview
Set Registry Preview as default .reg handler
Ensure .reg file is UTF-16 LE with BOM
Check file isn’t corrupted

Syntax Errors Shown

Common Issues:

Invalid registry path format
Incorrect value type syntax
Missing header line
Wrong encoding

Fixes:

Verify registry path follows HKEY_* format
Check value type syntax (dword:, hex:, etc.)
Ensure first line is “Windows Registry Editor Version 5.00”
Save file as UTF-16 LE with BOM

Changes Not Applying

Reasons:

Insufficient permissions (need admin for HKLM)
Registry key protected by policy
Syntax errors in .reg file
Application using registry key is running

Solutions:

Run Registry Preview as administrator
Check Group Policy restrictions
Fix validation errors before applying
Close applications using the registry keys

Hex Editor Issues

Problems:

Binary data not displaying correctly
Can’t edit hex values
Encoding problems

Fixes:

Verify data type is REG_BINARY or similar
Check hex editor mode is active
Ensure valid hex characters (0-9, A-F)
Restart Registry Preview

Best Practices

Safety Guidelines

Before Applying Changes:

Always review every change in Registry Preview
Create backup of affected registry keys
Research unfamiliar keys before modifying
Test in VM if possible
Document changes for future reference
Create restore point before major changes

File Management

Organizing .reg Files:

Use descriptive filenames
Add comments explaining what changes do
Version control for important configurations
Separate tweaks by category
Keep backup/restore pairs together

Editing Tips

Effective Registry Editing:

Work on copies, not original files
Validate syntax before applying
Test on non-production systems first
Export current state before changes
Use hex editor for binary data
Comment your modifications

Telemetry

Registry Preview collects minimal telemetry: From source /src/modules/registrypreview/RegistryPreview/Telemetry/:

RegistryPreviewEditorStartEvent.cs - Launch tracking
RegistryPreviewEditorStartFinishEvent.cs - Startup completion timing

Privacy

Telemetry data:

Application start/finish events
Timestamp of launches
No file content or registry data collected
Anonymous usage statistics only

Source Code

Location: /src/modules/registrypreview/

Main window: RegistryPreview/RegistryPreviewXAML/MainWindow.xaml.cs
UI library: RegistryPreviewUILib/
Hex editor: RegistryPreviewUILib/Controls/HexBox/
Clipboard helper: RegistryPreviewUILib/ClipboardHelper.cs
Telemetry: RegistryPreview/Telemetry/
Event handling: RegistryPreview/MainWindow.Events.cs
Utilities: RegistryPreview/MainWindow.Utilities.cs

Registry Preview is a WinUI 3 application that provides a safer alternative to directly importing .reg files into the Windows Registry.

Documentation Index

​Overview

​Activation

​Interface

​Main Window

​File Structure Display

​Value Types

​Features

​Syntax Highlighting

​Hex Editor

​Clipboard Integration

​File Operations

Open

Save

Import

Compare

​Safety Features

​Preview Before Apply

​Validation

​Use Cases

​Registry File Format

​.REG File Structure

​Format Details

​Advanced Features

​Window Placement Persistence

​Theme Support

​Title Bar Customization

​File Association

​Configuration

​Settings Location

​Appearance Options

​Editor Preferences

​Keyboard Shortcuts

​Troubleshooting

​Best Practices

​Telemetry

​Source Code

Overview

Activation

Interface

Main Window

File Structure Display

Value Types

Features

Syntax Highlighting

Hex Editor

Clipboard Integration

File Operations

Safety Features

Preview Before Apply

Validation

Use Cases

Registry File Format

.REG File Structure

Format Details

Advanced Features

Window Placement Persistence

Theme Support

Title Bar Customization

File Association

Configuration

Settings Location

Appearance Options

Editor Preferences

Keyboard Shortcuts

Troubleshooting

Best Practices

Telemetry

Source Code