Open previews instead of editors for configured file types and extensions with a preview command.

Features

Auto-open preview — Opens preview when you open a supported file
Auto-close preview — Closes the preview tab when the source tab closes
Preview-only mode — Reader mode: preview only, one file at a time
Diff-aware — Skips previews in git diff views (configurable)
Configurable types — previewur.languageIdsEnabled or command Previewur: Choose Preview File Types
Robust state tracking — Self-healing preview detection; reopens after manual close
Format-agnostic — Handles varied preview label formats ("Preview: file", "Preview file")

Installation

From a VSIX or development host; Marketplace id follows publisher.name (see package.json).

Commands

Command	Keybinding	Description
Toggle Previewur	`Ctrl+Shift+Alt+M`	Enable/disable
Toggle Preview-Only Mode	`Ctrl+Shift+Alt+P`	Reader mode
Choose Preview File Types	—	Multi-select picker
Configure Language Overrides	—	Set per-language behavior overrides

On Mac, use Cmd instead of Ctrl

Configuration

Language IDs, commands, and file extensions are auto-detected from installed extensions. When you first open a supported file type, Previewur automatically enables it and shows a notification with a link to customize settings.

{
  "previewur.active": true,
  "previewur.doNotEnableNewLanguages": false,
  "previewur.languageIdsEnabled": ["markdown", "asciidoc", "ansi"],
  "previewur.defaultOpenPreviewToSide": true,
  "previewur.defaultAutoClosePreview": true,
  "previewur.defaultOpenOnGitDiff": false,
  "previewur.defaultPreviewOnlyMode": false,
  "previewur.defaultPreserveEditorColumn": true,
  "previewur.languageIdsConfig": [
    {
      "languageId": "markdown",
      "label": "Markdown",
      "previewCommand": "markdown.showPreview",
      "previewToSideCommand": "markdown.showPreviewToSide",
      "fileExtensions": [".md", ".markdown"],
      "seen": "first-time",
      "openPreviewToSide": true,
      "autoClosePreview": true,
      "openOnGitDiff": false,
      "previewOnlyMode": false
    },
    {
      "languageId": "asciidoc",
      "label": "AsciiDoc",
      "previewCommand": "asciidoc.showPreview",
      "previewToSideCommand": "asciidoc.showPreviewToSide",
      "fileExtensions": [".adoc", ".asciidoc"],
      "seen": "first-time",
      "openPreviewToSide": false,
      "autoClosePreview": true,
      "openOnGitDiff": false,
      "previewOnlyMode": false
    },
    {
      "languageId": "ansi",
      "label": "ANSI Text",
      "previewCommand": "HNRobert.ansi-viewer.showPreview",
      "previewToSideCommand": "HNRobert.ansi-viewer.showPreviewToSide",
      "fileExtensions": [".ans", ".ansi"],
      "seen": "first-time",
      "openPreviewToSide": false,
      "autoClosePreview": false,
      "openOnGitDiff": false,
      "previewOnlyMode": true,
      "preserveEditorColumn": true
    }
  ]
}

Configuration Notes

Auto-detection: Extensions are scanned on startup; languages with preview commands are detected automatically
First-time notification: When opening a new file type for the first time, Previewur shows a notification with a settings link
Opt-out: Set doNotEnableNewLanguages: true to prevent auto-enabling new detected languages
Customization: Languages are added to languageIdsConfig automatically with seen: "first-time" marker
Minimal config: Only specify fields you want to override; defaults are used for omitted fields

Use the command Previewur: Configure Language Overrides to manage per-language settings via UI.

Setting	Default	Description
`previewur.active`	`true`	Master switch
`previewur.doNotEnableNewLanguages`	(omitted => `false`)	Prevent auto-enabling newly detected languages
`previewur.languageIdsEnabled`	`[]`	Which language IDs get auto-preview (auto-populated)
`previewur.languageIdsConfig`	`[]`	Per-language configuration (auto-populated from scanned extensions)
`previewur.defaultOpenPreviewToSide`	`true`	Preview beside source (overridable via languageIdsConfig)
`previewur.defaultAutoClosePreview`	`true`	Close preview when source closes (overridable; ignored when `defaultPreviewOnlyMode`)
`previewur.defaultOpenOnGitDiff`	`false`	Open preview in git diff (overridable)
`previewur.defaultPreviewOnlyMode`	`false`	Preview-only reader mode — overrides `defaultPreserveEditorColumn` and `defaultAutoClosePreview` (overridable)
`previewur.defaultPreserveEditorColumn`	`true`	Keep focus on source column after preview opens — prevents other files from opening in the preview column (overridable; ignored when `defaultPreviewOnlyMode`)

languageIdsConfig Structure

Each entry in languageIdsConfig supports:

Field	Required	Description
`languageId`	Yes	VS Code language identifier
`label`	No	Display name (defaults to languageId)
`previewCommand`	No	Command for same-group preview
`previewToSideCommand`	No	Command for side-by-side preview
`fileExtensions`	No	File extensions for this language
`seen`	No	Internal marker for first-time notification (auto-set)
`openPreviewToSide`	No	Override default placement
`autoClosePreview`	No	Override auto-close behavior (ignored when `previewOnlyMode`)
`openOnGitDiff`	No	Override git diff behavior
`previewOnlyMode`	No	Override reader mode
`preserveEditorColumn`	No	Override source-column focus behavior (ignored when `previewOnlyMode`)

Technical Implementation

Preview State Management

Previewur maintains robust tracking of opened previews with self-healing validation:

Stale detection — Validates preview existence before blocking reopens; auto-clears stale entries
Multiple entry points — Handles onDidOpenTextDocument, onDidChangeActiveTextEditor, and tab events
Preview-only mode support — Correctly reopens in reader mode after manual close
Webview tab tracking — Monitors preview tab closures to maintain accurate state
Flexible label matching — Supports multiple preview label formats from different extensions