Offline Markdown Preview (Beta)

Offline Markdown preview for VS Code with Mermaid diagrams, KaTeX math, secure local rendering, export, scroll sync, and outline navigation.

Early release note: Marketplace listing details are still being finalized.

Offline + Secure: runs locally inside VS Code and the extension does not send your Markdown contents anywhere (no cloud, no telemetry).

TODO: Add GitHub Actions and VS Code Marketplace badges (repo is live: Bowlerr/offline-markdown-preview) after the publisher/item ID is set.

GIF Demos

A quick tour of the main workflows (all offline, inside VS Code):

Live preview + scroll sync TODO: add GIF/screenshot in images/	Mermaid + math rendering TODO: add GIF/screenshot in images/
Outline + heading navigation TODO: add GIF/screenshot in images/	HTML/PDF export TODO: add GIF/screenshot in images/

What You Get

• Free: no paywalls; MIT-licensed.
• Offline + secure by design: render/preview/export works locally with bundled libraries (no CDN, no remote fonts, no telemetry).
• Secure webview defaults: strict CSP + HTML sanitization (DOMPurify) enabled by default.
• Markdown preview panel with live updates and editor/preview scroll sync.
• Bundled rendering stack: Mermaid diagrams, KaTeX math, Prism syntax highlighting.
• Navigation tools: Markdown outline TreeView, heading quick pick, copy heading links.
• Export tools: HTML export and PDF export from the preview workflow.
• Safety controls: external-link confirmation, image size limits, sanitization toggle (with explicit unsafe wording).

Quick Start

1. Open a Markdown file (.md) in VS Code.
2. Run Offline Markdown Preview: Open Preview (or Open Preview To Side).
3. Use the outline view and heading commands to navigate larger documents.
4. Export when needed with Export HTML or Export PDF.

Tip: use the editor title action to open preview to the side while editing.

Privacy, Offline, and Data Safety

• No network required for render, preview, or export.
• No telemetry and no document-content upload.
• Remote web requests are blocked in the webview runtime (fetch, XMLHttpRequest, WebSocket, EventSource) for http(s) targets.
• Strict CSP includes connect-src 'none'.
• Sanitization is on by default (offlineMarkdownViewer.sanitizeHtml = true).
• Export writes files only on explicit user action (HTML/PDF commands).

Settings

These VS Code settings control rendering, safety, and performance:

• offlineMarkdownViewer.enableMermaid (default: true): enable Mermaid rendering (bundled locally).
• offlineMarkdownViewer.enableMath (default: true): enable KaTeX math rendering (bundled locally).
• offlineMarkdownViewer.scrollSync (default: true): synchronize editor and preview scrolling.
• offlineMarkdownViewer.sanitizeHtml (default: true): sanitize rendered HTML in the webview; turning this off is unsafe.
• offlineMarkdownViewer.externalLinks.confirm (default: true): confirm before opening external links.
• offlineMarkdownViewer.preview.maxImageMB (default: 8): maximum local image size loaded into preview.
• offlineMarkdownViewer.export.embedImages (default: false): embed local images as data URIs for HTML export (privacy warning shown).
• offlineMarkdownViewer.performance.debounceMs (default: 120): debounce delay for live preview updates.
• offlineMarkdownViewer.preview.customCssPath (default: ""): workspace-local CSS file appended to preview output.
• offlineMarkdownViewer.preview.showFrontmatter (default: false): show parsed YAML frontmatter above the rendered document.

Commands

Command	Purpose
Offline Markdown Preview: Open Preview	Open the Markdown preview panel
Offline Markdown Preview: Open Preview To Side	Open the preview beside the active editor
Offline Markdown Preview: Export HTML	Export the current preview/document as HTML
Offline Markdown Preview: Export PDF	Export the current preview/document as PDF
Offline Markdown Preview: Toggle Scroll Sync	Enable/disable editor <-> preview scroll sync
Offline Markdown Preview: Copy Heading Link	Copy a heading anchor link (outline context)
Offline Markdown Preview: Quick Pick Heading	Jump to a heading via quick pick

Keybindings (VS Code)

No extension-level VS Code keybindings are registered by default (nothing is contributed in package.json). You can add your own command shortcuts in VS Code if desired.

Preview-local shortcuts (when focus is inside the preview webview):

• Cmd/Ctrl+F: open/focus preview search
• Enter (in search box): next match

Notes, Limits, and Safety

• Sanitization can be disabled for advanced cases, but this is unsafe for untrusted Markdown/HTML content.
• Paths outside the workspace may be blocked for preview safety when resolving local resources.
• Large images are capped by offlineMarkdownViewer.preview.maxImageMB to avoid excessive memory usage in preview.
• Custom CSS must be workspace-local and .css only; user/global settings are ignored for safety.
• PDF export behavior depends on the VS Code/webview print route and may vary slightly by platform.

Troubleshooting

• Mermaid not rendering: verify offlineMarkdownViewer.enableMermaid is enabled; invalid Mermaid syntax falls back to code/plain output.
• Math not rendering: verify offlineMarkdownViewer.enableMath is enabled; invalid expressions render as plain text fallback.
• Images missing: check workspace path restrictions and offlineMarkdownViewer.preview.maxImageMB for large local images.
• Custom CSS not applied: ensure the path is workspace-local, ends with .css, and is set in workspace settings (not user settings).
• External links are blocked/prompting: this is expected; review offlineMarkdownViewer.externalLinks.confirm and use explicit link opens.

Changelog

See CHANGELOG.md.

License

MIT License - see LICENSE.

Credits

See CREDITS.md for maintainer and bundled-library credits.