AXSG Language Server (VS Code)
VS Code extension for AXSG XAML/AXAML language service.
By default, the extension runs a bundled managed language server:
dotnet <extension>/server/XamlToCSharpGenerator.LanguageServer.dll
You can switch to a custom executable with:
axsg.languageServer.mode = "custom"axsg.languageServer.command = "..."axsg.languageServer.args = [...]
The extension also adds a status bar item ($(info) AXSG) that shows language-server status.
Click it to view runtime info and open the output channel.
When metadata symbols include SourceLink debug information, navigation opens a virtual source document (axsg-sourcelink://) fetched from the mapped URL.
Avalonia preview is available from AXSG: Open Avalonia Preview in the command palette, editor title, or XAML editor context menu.
The preview command launches Avalonia's designer host through a bundled AXSG bridge. In auto mode the extension prefers AXSG source-generated preview when the project output contains XamlToCSharpGenerator.Runtime.Avalonia, and falls back to Avalonia's XamlX previewer otherwise.
Semantic highlighting is enabled for .xaml and .axaml with a Visual Studio-style XAML palette:
- blue delimiters/attribute values/keywords
- red element and attribute names
- teal namespace prefixes
- green comments
- cyan markup-extension class identifiers
Avalonia Preview
Preview sessions require a previewable Avalonia executable project in the workspace.
If the current XAML file belongs to a library, set axsg.preview.hostProject to the Avalonia app project that should host the preview.
Preview compiler modes:
auto: prefer AXSG source-generated preview when available, otherwise use Avalonia/XamlXsourceGenerated: force AXSG source-generated preview; this is the default mode, it keeps live unsaved XAML edits in sync in the preview, and save/build refresh keeps the generated baseline aligned when axsg.preview.buildBeforeLaunch is enabledavalonia: force Avalonia's official XamlX previewer and keep live unsaved XAML updates
Build behavior is optimized for preview latency:
- preview startup reuses existing host/source outputs when they are already usable
- source-generated save refresh rebuilds only the source project when the host app output can be reused
- preview builds use
--no-restore when the project is already restored and fall back to a normal build only if restore is actually required
Relevant settings:
axsg.preview.dotNetCommandaxsg.preview.compilerModeaxsg.preview.targetFrameworkaxsg.preview.hostProjectaxsg.preview.buildBeforeLaunchaxsg.preview.autoUpdateDelayMs
axsg.preview.compilerMode = auto is the default. It prefers source-generated preview first and falls back to Avalonia/XamlX when needed without treating the fallback path as an error.
MCP and Preview Hosts
The extension does not require you to start an MCP server for normal editing or preview usage.
Current behavior:
- the extension owns the bundled language-server startup path
- the preview UI uses the bundled preview helper transport for the product workflow
- the same preview helper also supports
--mcp for custom clients, tests, and future remote integrations
Separate AXSG MCP surfaces are available when you need them outside the extension:
- workspace MCP host:
axsg-mcp --workspace /path/to/workspace
- runtime MCP host: embed
XamlSourceGenRuntimeMcpServer into the running app
- preview MCP host:
dotnet <preview-host>/XamlToCSharpGenerator.PreviewerHost.dll --mcp
The preview MCP host now exposes:
axsg.preview.startaxsg.preview.hotReloadaxsg.preview.updateaxsg.preview.stop
Use axsg.preview.hotReload when a custom client needs the in-process live preview result instead of dispatch-only update acceptance.
For the operational host matrix and dotnet watch guidance, see:
Development
npm install
npm run prepare:server
npm test
npx @vscode/vsce package
Install generated VSIX via VS Code command palette: Extensions: Install from VSIX....
