File Explorer Add-ons

Preview and thumbnail handlers for additional file types in Windows File Explorer

Overview

File Explorer Add-ons extend Windows File Explorer with preview and thumbnail support for file types not natively supported by Windows. View file contents directly in the preview pane without opening external applications.

File Explorer Add-ons work with Windows File Explorer’s built-in preview pane (Alt+P to toggle).

Activation

1. Enable File Explorer Add-ons

   Open PowerToys Settings and navigate to File Explorer section

2. Enable Individual Handlers

   Toggle on the preview handlers you want to use

3. Show Preview Pane

   In File Explorer, press Alt+P or click View → Preview pane

4. Select File

   Click on a supported file to see preview

Key Features

Supported File Types

Code Files

Monaco Preview Handler

Syntax-highlighted code preview

.cs, .cpp, .py, .js, .ts, .json, .xml, .html, .css, .md, .sql

Markdown

Markdown Preview Handler

Rendered Markdown documents

.md, .markdown

SVG Images

SVG Preview & Thumbnail

Vector graphics preview

.svg files

PDF Documents

PDF Preview & Thumbnail

PDF document preview

.pdf files

G-code

G-code Preview & Thumbnail

3D printing code preview

.gcode, .bgcode files

STL Models

STL Thumbnail

3D model thumbnails

.stl files

QOI Images

QOI Preview & Thumbnail

“Quite OK Image” format

.qoi files

Preview Handlers

Preview handlers display file contents in the preview pane:

Monaco Code Preview

Features:

• Syntax highlighting
• Line numbers
• Multiple language support
• Read-only view

Supported languages:

• C/C++/C#
• Python
• JavaScript/TypeScript
• JSON/XML
• HTML/CSS
• Markdown
• SQL
• And 50+ more

Implementation: Uses Monaco Editor (VS Code’s editor)

Markdown Preview

Features:

• Rendered HTML output
• Supports GFM (GitHub Flavored Markdown)
• Code blocks with syntax highlighting
• Tables, lists, images
• Links (clickable in preview)

Supported elements:

• Headers, paragraphs, lists
• Code blocks with syntax highlighting
• Tables and blockquotes
• Images and links

PDF Preview

Features:

• Page rendering
• Zoom support
• Multi-page documents
• Text selection

Note: Basic preview functionality. For advanced features, open in full PDF reader.

SVG Preview

Features:

• Vector rendering
• Scalable display
• Preserves quality
• Supports animations

File types:

• .svg (Scalable Vector Graphics)
• Embedded in HTML

G-code Preview

Features:

• 3D toolpath visualization
• Layer view
• Code syntax highlighting
• Print time/filament estimates

Formats:

• .gcode (standard G-code)
• .bgcode (binary G-code)

Thumbnail Providers

Generate thumbnails for File Explorer icon view:

// Thumbnail provider interface implementation
class ThumbnailProvider : public IThumbnailProvider
{
public:
    // Generate thumbnail from file
    HRESULT GetThumbnail(
        UINT cx,              // Requested width
        HBITMAP *phbmp,       // Output bitmap
        WTS_ALPHATYPE *pdwAlpha  // Alpha channel type
    );
};

Supported:

• SVG Thumbnail: Rasterized vector graphics
• PDF Thumbnail: First page preview
• STL Thumbnail: 3D model render
• G-code Thumbnail: Embedded preview image or toolpath
• QOI Thumbnail: Decoded QOI image

Configuration

Enable/Disable Handlers

Individually control each preview handler:

monaco_preview · boolean · default: "false"

Enable Monaco code preview handler

Performance note: May be slower for very large files

markdown_preview · boolean · default: "false"

Enable Markdown preview handler

svg_preview · boolean · default: "false"

Enable SVG preview handler

svg_thumbnail · boolean · default: "false"

Enable SVG thumbnail provider

pdf_preview · boolean · default: "false"

Enable PDF preview handler

pdf_thumbnail · boolean · default: "false"

Enable PDF thumbnail provider

gcode_preview · boolean · default: "false"

Enable G-code preview handler

gcode_thumbnail · boolean · default: "false"

Enable G-code thumbnail provider

stl_thumbnail · boolean · default: "false"

Enable STL 3D model thumbnail provider

qoi_preview · boolean · default: "false"

Enable QOI image preview handler

qoi_thumbnail · boolean · default: "false"

Enable QOI image thumbnail provider

File Association

Preview handlers register for specific file extensions in Windows registry:

HKEY_CLASSES_ROOT\.md
  └─ shellex
      └─ {8895b1c6-b41f-4c1c-a562-0d564250836f}
          = "{CLSID of MarkdownPreviewHandler}"

Automatic registration: PowerToys installer handles registration

Use Cases

Software Development

Code Review

Quick preview of source code files:

1. Enable Monaco preview handler
2. Navigate to project directory
3. Click files to preview without opening IDE
4. Review code changes quickly

Benefits:

• Syntax highlighting
• No need to open full editor
• Fast file browsing

Documentation

Preview README and documentation:

• Enable Markdown preview
• Click README.md to see rendered output
• Review docs before editing
• Verify formatting

Configuration Files

Preview JSON, XML, YAML configs:

File Explorer
├─ config.json        ← Click to preview
├─ appsettings.json   ← Syntax highlighted
└─ package.json       ← Formatted JSON

Design & Graphics

1. SVG Management

   Enable SVG preview and thumbnails

   Browse icon libraries visually

2. Quick Preview

   Click SVG files to see vector graphics

   No need to open design software

3. Batch Review

   Use thumbnail view to see all SVGs

   Find icons quickly

3D Printing

G-code Inspection

Preview G-code files before printing

• View toolpath
• Check layer heights
• Estimate print time

Model Thumbnails

STL thumbnail generation

• Visual model previews
• Browse models easily
• Identify files quickly

Document Management

PDF Preview

Quick document review:

1. Enable PDF preview
2. Browse document folders
3. Click PDFs to preview
4. No need to open full PDF reader

Use cases:

• Invoice review
• Document selection
• Quick reference

Markdown Notes

Personal knowledge base:

• Keep notes in Markdown
• Preview formatted output
• Browse notes visually
• Quick reference

Technical Details

Architecture

Preview Handler Structure

src/modules/previewpane/
├─ MonacoPreviewHandler/
│   ├─ MonacoPreviewHandler.cpp     # C++ wrapper
│   └─ MonacoPreviewHandlerControl/  # .NET implementation
├─ MarkdownPreviewHandler/
│   ├─ MarkdownPreviewHandler.cpp
│   └─ MarkdownPreviewHandlerControl/
├─ SvgPreviewHandler/
├─ PdfPreviewHandler/
├─ GcodePreviewHandler/
└─ common/                      # Shared utilities

Source: src/modules/previewpane/README.md

Preview Handler Process

Preview handlers run in isolated process:

// Preview handler isolation
// Handlers run in prevhost.exe surrogate process
// Protects File Explorer from crashes
// Each handler in separate AppDomain/.NET process

Benefits:

• Crash isolation
• Memory management
• Security sandboxing

Implementation Pattern

Typical handler implementation:

// C++ Preview Handler Interface
class PreviewHandler : 
    public IPreviewHandler,
    public IInitializeWithStream,
    public IOleWindow
{
public:
    // Load file content
    HRESULT Initialize(IStream* pstream, DWORD grfMode);
    
    // Create preview window
    HRESULT SetWindow(HWND hwnd, const RECT* prc);
    
    // Render preview
    HRESULT DoPreview();
    
    // Cleanup
    HRESULT Unload();
};

Keyboard Shortcuts

File Explorer

Shortcut	Action
Alt+P	Toggle preview pane
Arrow Up/Down	Navigate files (preview updates)
Enter	Open file in default application
Ctrl+Scroll	Zoom thumbnail size

Troubleshooting

Preview not showing

Check:

• Preview pane is visible (Alt+P)
• Specific handler is enabled in PowerToys Settings
• File extension is supported
• File is not locked/in use

Fix:

1. Restart File Explorer (Task Manager → Windows Explorer → Restart)
2. Disable and re-enable handler
3. Restart PowerToys

Thumbnails not generating

Possible causes:

• Thumbnail cache corrupted
• Handler not enabled
• File too large

Solutions:

1. Enable thumbnail provider in settings
2. Clear thumbnail cache:
   del /f /s /q /a %LocalAppData%\Microsoft\Windows\Explorer\thumbcache_*.db
   
3. Restart File Explorer

Monaco preview slow for large files

Performance issue:

• Monaco handler loads entire file
• Large files (>1MB) may be slow

Workaround:

• Disable Monaco handler for large files
• Use external editor for large files
• Consider file size limits in settings (if available)

Preview shows error or blank

Debug:

1. Check file is not corrupted
2. Try opening in native application
3. Check PowerToys logs:
   %LOCALAPPDATA%\Microsoft\PowerToys\Logs
   
4. Look for preview handler errors

Common issues:

• File encoding not supported
• Missing dependencies
• File format variation not supported

See Also

• File Locksmith - Unlock files in use
• PowerToys Run - Quick file search
• Image Resizer - Batch image operations