MDViewer+

A native, offline macOS Markdown editor and viewer with live preview.

MDViewer+ 2.1.0 ships from one source tree in two editions:

	Lite	Full
Recommended for	Minimum footprint	Most users
Shared native features	Folder Navigator, Find, Quick Open, secure internal links, folder watcher, outline, editing, printing	Same
Shared Markdown features	Footnotes, alerts, tasks, image zoom, code controls	Same
Code highlighting	Custom Prism: Swift, JavaScript/TypeScript, JSON, Bash, Python, Rust, HTML, CSS	Lazy highlight.js common-language bundle
Metadata	Raw Markdown	Lazy safe YAML frontmatter card
Diagrams	—	Lazy offline Mermaid with svg-pan-zoom

Both editions use the same bundle identifier, application name, document associations, sandbox, and native DocumentGroup lifecycle. Installing one edition replaces the other. Full is the recommended download.

Highlights

• View, split, and edit modes with responsive live preview
• Bidirectional editor/preview scroll synchronization
• Focus-aware Find: native NSTextView Find in the editor and WKWebView.find in the preview
• Current-folder Quick Open with deterministic, dependency-free matching
• An optional, read-only Folder Navigator across View, Split, and Edit modes
• Secure relative Markdown links opened through the native document lifecycle
• Debounced native folder events; no polling or background index
• Searchable transient document outline with duplicate and Unicode heading IDs
• Footnotes, GitHub alerts, read-only task lists, local image inspection, and accessible code-block controls
• Eight coordinated light/dark themes and context-aware zoom
• Dedicated print rendering that waits for images and Full lazy renderers
• No rendered-content network access, runtime downloads, Electron, Swift packages, or third-party native frameworks

Editions and offline rendering

Lite physically excludes Mermaid, svg-pan-zoom, highlight.js, js-yaml, and their notices. Full physically excludes Prism. Full modules are served only from a generated app-bundle allowlist and are imported on demand:

• highlight.js only when a non-Mermaid code fence exists
• js-yaml only when the document begins with a valid frontmatter delimiter
• Mermaid only for fenced mermaid blocks
• svg-pan-zoom only after a diagram renders successfully

Ordinary Markdown in Full initializes none of these modules.

Install

Download one of the signed and notarized release artifacts:

• MDViewerPlus-Full-macos.dmg — recommended
• MDViewerPlus-Lite-macos.dmg — minimum footprint

Every DMG has a matching .sha256 file.

To build locally:

brew install xcodegen
xcodegen generate
xcodebuild -scheme MDViewerPlus-Lite -configuration Release build
xcodebuild -scheme MDViewerPlus-Full -configuration Release build

Keyboard shortcuts

Action	Shortcut
Find / next / previous	Cmd F / Cmd G / Cmd Shift G
Quick Open	Cmd K
Show or hide Folder Navigator	Cmd Shift B
Document Outline	Cmd Shift O
Toggle View Mode	Cmd E
Bold / Italic / Link	Cmd B / Cmd I / Cmd Shift K
Print	Cmd P
Previous / next Markdown file	Cmd Option Left / Cmd Option Right
Reload	Cmd R
Zoom in / out / actual size	Cmd + / Cmd - / Cmd 0
System / light / dark appearance	Cmd Shift 0 / Cmd Shift 1 / Cmd Shift 2
Help	Cmd ?

Help and support

Choose Help > MDViewer+ Help for the native in-app guide. About MDViewer+ shows the installed Lite or Full edition, version, and build.

• MDViewer+ website
• Source and documentation
• Report an issue

Security model

• Release builds use App Sandbox and Hardened Runtime.
• The Folder Navigator is local-only, collapsed by default, and uses an explicitly authorized current or ancestor folder. Choose File > Open Folder… to change its root and Navigate > Reveal Current Document in Folder Navigator to locate the open file.
• Folder contents load one directory at a time. Hidden items, packages, symbolic links, non-regular files, and files other than .md, .markdown, .mdown, and .mkd are excluded. Enumeration is bounded to depth 12, 500 direct children, and 5,000 loaded items. Native filesystem events refresh only directories that are already loaded.
• Opening from the navigator uses the normal document lifecycle. A clean source window closes after a successful open; a source window with unsaved edits stays open, and failures never discard edited text.
• WebKit requires the sandbox network-client entitlement to launch its content process, but the render-page CSP blocks all connections and remote resources.
• A restrictive CSP blocks network connections, frames, objects, workers, forms, base navigation, remote images, and untrusted scripts.
• Markdown HTML is sanitized by a narrow DOMPurify policy before insertion.
• Highlighter output and Mermaid SVG use separate constrained sanitizers.
• Local resources are limited to raster images under a user-authorized folder; symlink escapes and unsupported types are rejected.
• Internal links accept only supported relative Markdown files under that folder. Absolute paths, queries, traversal, encoded traversal, unsupported extensions, directories, and symlink escapes are rejected.
• YAML uses FAILSAFE_SCHEMA plus source, depth, node, collection, key, and display limits. Unsafe tags and prototype-related keys are rejected.
• Mermaid uses strict security, disabled HTML labels, bounded source/count/ concurrency/time, generation cancellation, and no remote resources.

Dependencies and measured web assets

Library	Version	Edition	License
marked	15.0.7	Common	MIT
DOMPurify	3.4.12	Common	Apache-2.0 OR MPL-2.0
marked-footnote	1.4.0	Common	MIT
Prism	1.30.0	Lite	MIT
highlight.js	11.11.1	Full	BSD-3-Clause
js-yaml	5.2.3	Full	MIT
Mermaid	11.16.0	Full	MIT
svg-pan-zoom	3.6.2	Full	BSD-2-Clause

vendor/manifest.json records every shipped file's SHA-256, exact package version, source, license, and edition. THIRD-PARTY-NOTICES.md and the bundled license files contain the corresponding notices.

As of 2026-08-09, npm audit reports two moderate upstream advisories without a published fixed release. MDViewer+ never enables DOMPurify IN_PLACE; Mermaid uses trusted configuration, bounded/concurrent/timed rendering, and separately sanitized SVG. There are no high or critical audit findings.

The generated Lite-only Prism asset is 31.6 KiB minified. This is above the original approximate 10–20 KiB target because all eight promised language families and their required Prism grammar dependencies are retained; Lite still has no plugins, autoloader, theme asset, or Full dependency. The source and bundle audits enforce a 36 KiB Lite-only ceiling and physical exclusions.

Test and release

scripts/vendor_web_assets.sh  # deterministic assets, hashes, notices
scripts/test_editions.sh      # all unit/render/security tests in both editions

REQUIRE_SIGNING=0 EDITION=lite scripts/build_release.sh
REQUIRE_SIGNING=0 EDITION=full scripts/build_release.sh
scripts/audit_bundle.sh lite dist/lite/MDViewer+.app
scripts/audit_bundle.sh full dist/full/MDViewer+.app

For a signed local release, copy .release.env.example to .release.env and run scripts/release_macos.sh. It builds, audits, packages, notarizes, staples, Gatekeeper-checks, and hashes both editions.

License

MIT