NotepadLite

NotepadLite is a lightweight Windows desktop text editor written in C#. The current implementation starts with a fast WPF shell, a UI-independent document core, and a syntax-definition pipeline that loads a practical subset of Notepad++ user-defined language XML files from disk.

Current Scope

• WPF desktop shell targeting net10.0-windows
• Open, edit, save, and save-as workflows
• AvalonEdit-based text surface with line numbers
• Runtime language-definition loading from built-in and user folders
• Import of a documented subset of Notepad++ UDL XML

Project Layout

• src/NotepadLite.App contains the WPF shell and editor integration.
• src/NotepadLite.Core contains document and file services.
• src/NotepadLite.Syntax contains the language-definition model and UDL importer.
• tests/NotepadLite.Syntax.Tests contains automated tests for the importer.
• assets/languages contains built-in sample language definitions copied into the app output.

Build And Run

dotnet restore NotepadLite.slnx
dotnet build NotepadLite.slnx
dotnet run --project src/NotepadLite.App/NotepadLite.App.csproj

To open a file directly at startup:

dotnet run --project src/NotepadLite.App/NotepadLite.App.csproj -- "C:\path\to\file.json"

Test

dotnet test NotepadLite.slnx

Build Installer

The repository includes a self-contained Windows installer package. Running the packaged installer copies the app to C:\Program Files\NotepadLite, registers an uninstall entry, creates a Start menu shortcut, and adds a Windows Explorer right-click command named Open with NotepadLite for all files.

Build the installer package with:

powershell -ExecutionPolicy Bypass -File .\scripts\build-installer.ps1

Outputs:

• Published application files: artifacts\publish\NotepadLite\win-x64
• Installer package folder: artifacts\installer\NotepadLite
• Installer archive: artifacts\installer\NotepadLite-Installer.zip

To install on a machine, open artifacts\installer\NotepadLite and run Install-NotepadLite.cmd. The installer will request elevation because it installs machine-wide.

Adding Language Definitions

Built-in language definitions are copied from assets/languages into the app output under Assets/Languages.

User-added definitions can be dropped into:

%LocalAppData%\NotepadLite\Languages

The current importer supports:

• name and ext on UserLang
• keyword groups under Keywords
• operators from a Keywords entry named Operators
• line comments and block comments from Comments
• symmetric string delimiters from Delimiter elements

The current importer does not attempt full Notepad++ compatibility. Unsupported constructs are reported in the diagnostics area instead of being silently approximated.

Windows Context Menu

Windows Explorer can launch the editor from a file right-click menu once the app accepts a file path argument. The installer package now creates this integration automatically.

If you need a manual fallback after copying the app to a stable path, use scripts/notepadlite-context-menu.reg, which points to the default installer location.

Example .reg content:

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Classes\*\shell\OpenWithNotepadLite]
@="Open with NotepadLite"
"Icon"="C:\\Program Files\\NotepadLite\\NotepadLite.App.exe"

[HKEY_CURRENT_USER\Software\Classes\*\shell\OpenWithNotepadLite\command]
@="\"C:\\Program Files\\NotepadLite\\NotepadLite.App.exe\" \"%1\""

Notes:

• Replace the executable path if you install the app elsewhere.
• The installer package uses a machine-wide registration under HKEY_LOCAL_MACHINE, while the .reg file uses HKEY_CURRENT_USER as a no-installer fallback.