> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/microsoft/powertoys/llms.txt
> Use this file to discover all available pages before exploring further.

# Registry Preview

> A visual editor for Windows Registry files (.reg) that lets you review and edit registry changes before applying them.

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

<Steps>
  <Step title="Open Registry File">
    Double-click a `.reg` file or right-click and choose "Open with Registry Preview."
  </Step>

  <Step title="Review Changes">
    Examine the registry keys, values, and data that will be modified.
  </Step>

  <Step title="Edit if Needed">
    Make changes to registry values directly in Registry Preview.
  </Step>

  <Step title="Apply or Save">
    Apply changes to registry or save as modified .reg file.
  </Step>
</Steps>

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

## Interface

### Main Window

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

<CodeGroup>
  ```csharp Main Window theme={null}
  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; }
  }
  ```
</CodeGroup>

Features:

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

### File Structure Display

<Tabs>
  <Tab title="Tree View">
    Registry keys displayed in hierarchical tree:

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

    * Expandable/collapsible nodes
    * Visual hierarchy
    * Key path navigation
  </Tab>

  <Tab title="List View">
    Registry values shown in detail:

    | Name          | Type       | Data                 |
    | ------------- | ---------- | -------------------- |
    | (Default)     | REG\_SZ    | (value not set)      |
    | EnableFeature | REG\_DWORD | 0x00000001 (1)       |
    | InstallPath   | REG\_SZ    | C:\Program Files\App |
  </Tab>
</Tabs>

### Value Types

Registry Preview displays all registry value types:

<Accordion title="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
</Accordion>

## 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/`

<Accordion title="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
</Accordion>

### Clipboard Integration

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

<Accordion title="Clipboard Operations">
  * Copy registry keys
  * Copy values and data
  * Paste registry snippets
  * Export selections to clipboard
</Accordion>

### File Operations

<CardGroup cols={2}>
  <Card title="Open" icon="folder-open">
    * Open .reg files
    * Recent files list
    * Drag and drop support
    * Command-line arguments
  </Card>

  <Card title="Save" icon="floppy-disk">
    * Save modifications
    * Save as new file
    * Export selected keys
    * Backup before apply
  </Card>

  <Card title="Import" icon="file-import">
    * Apply to registry
    * Preview before import
    * Undo support
    * Backup creation
  </Card>

  <Card title="Compare" icon="code-compare">
    * Compare two .reg files
    * Highlight differences
    * Merge changes
    * Conflict resolution
  </Card>
</CardGroup>

## Safety Features

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

### Preview Before Apply

<Steps>
  <Step title="Open Registry File">
    Load .reg file in Registry Preview.
  </Step>

  <Step title="Review All Changes">
    Examine every key and value that will be modified.
  </Step>

  <Step title="Understand Impact">
    Research unfamiliar registry keys before applying.
  </Step>

  <Step title="Create Backup">
    Export current registry state for affected keys.
  </Step>

  <Step title="Apply Changes">
    Only after thorough review, apply changes.
  </Step>
</Steps>

### Validation

<Accordion title="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.
</Accordion>

## Use Cases

<AccordionGroup>
  <Accordion title="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.
  </Accordion>

  <Accordion title="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.
  </Accordion>

  <Accordion title="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.
  </Accordion>

  <Accordion title="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.
  </Accordion>

  <Accordion title="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.
  </Accordion>
</AccordionGroup>

## Registry File Format

### .REG File Structure

<CodeGroup>
  ```registry Example .reg File theme={null}
  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"=-
  ```
</CodeGroup>

### Format Details

<Tabs>
  <Tab title="Header">
    All .reg files must start with:

    ```registry theme={null}
    Windows Registry Editor Version 5.00
    ```

    This identifies the file format (Windows 2000 and later).
  </Tab>

  <Tab title="Keys">
    Registry keys in square brackets:

    ```registry theme={null}
    [HKEY_LOCAL_MACHINE\Software\Company\Product]
    ```

    To delete a key, prefix with minus:

    ```registry theme={null}
    [-HKEY_CURRENT_USER\Software\OldApp]
    ```
  </Tab>

  <Tab title="Values">
    Value format: `"Name"=type:data`

    **String (REG\_SZ):**

    ```registry theme={null}
    "AppName"="My Application"
    ```

    **DWORD (32-bit):**

    ```registry theme={null}
    "Version"=dword:00000001
    ```

    **QWORD (64-bit):**

    ```registry theme={null}
    "LargeValue"=hex(b):01,00,00,00,00,00,00,00
    ```

    **Binary:**

    ```registry theme={null}
    "Data"=hex:00,01,02,03,04,05
    ```

    **Multi-String (REG\_MULTI\_SZ):**

    ```registry theme={null}
    "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:

    ```registry theme={null}
    "OldValue"=-
    ```
  </Tab>

  <Tab title="Comments">
    Lines starting with semicolon are comments:

    ```registry theme={null}
    ; This is a comment
    ; Comments are ignored when importing
    ```
  </Tab>
</Tabs>

## Advanced Features

### Window Placement Persistence

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

<Accordion title="Window State Management">
  Registry Preview saves window position and size:

  ```csharp theme={null}
  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
</Accordion>

### 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`:

```csharp theme={null}
// 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

<Accordion title="Settings Storage">
  Registry Preview settings stored at:

  ```
  %LOCALAPPDATA%\Microsoft\PowerToys\RegistryPreview\
  ```

  Files:

  * `app-placement.json` - Window position and size
  * User preferences and recent files
</Accordion>

### 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

<AccordionGroup>
  <Accordion title="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
  </Accordion>

  <Accordion title="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
  </Accordion>

  <Accordion title="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
  </Accordion>

  <Accordion title="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
  </Accordion>
</AccordionGroup>

## Best Practices

<AccordionGroup>
  <Accordion title="Safety Guidelines">
    **Before Applying Changes:**

    1. **Always review** every change in Registry Preview
    2. **Create backup** of affected registry keys
    3. **Research unfamiliar keys** before modifying
    4. **Test in VM** if possible
    5. **Document changes** for future reference
    6. **Create restore point** before major changes
  </Accordion>

  <Accordion title="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
  </Accordion>

  <Accordion title="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
  </Accordion>
</AccordionGroup>

## Telemetry

Registry Preview collects minimal telemetry:

From source `/src/modules/registrypreview/RegistryPreview/Telemetry/`:

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

<Accordion title="Privacy">
  Telemetry data:

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

## 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`

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