A local-first Markdown editor and viewer with live preview.
Open, write, organize, review, render, export, and optionally share Markdown in a browser, as a Progressive Web App (PWA), in Docker, or in the Neutralino desktop application.
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What Markdown Viewer Does
Markdown Viewer is an open source, local-first workspace for developers, writers, students, researchers, and anyone working with .md or .markdown files. Go beyond plain text. Organize multiple documents, review with anchored comments without changing the Markdown, and render diagrams, maps, charts, math, 3D models, and music—all in one focused workspace.
Turn a document into a Share Snapshot link for quick handoffs, or start access-controlled Live Share for real-time co-editing, live cursors, anchored comments, and threaded replies. Everyday editing stays on your device. No account is required, and the application includes no ads, analytics, telemetry, or subscriptions.
Highlights
- Workspace and documents: organize naturally sorted documents and folders with per-document IndexedDB storage on the web; use Recent, Favorites, search, tabs, bulk actions, an encrypted Secret Workspace, and a 30-day Trash. The desktop app can also link external Markdown files and folders beside independent Vault copies, keeping automatic recovery drafts separate from explicit writes to originals. Middle-click a tab to close it without deleting its saved document.
- Backup and restore: export or import a folder-preserving workspace ZIP; encrypted Secret Workspace files are optional, while trash, desktop history, and recovery journals stay outside the backup. Desktop backups can recover linked drafts but never silently restore write access to external paths.
- Editing and review: switch among Editor, Split view, and Preview; type
/ at the start of a line for searchable block commands; browse categorized GitHub emojis; use formatting tools, an 8×8 quick table selector, productivity shortcuts, custom undo/redo, Find and Replace, LTR/RTL direction, smooth Page Up/Down navigation, pane-scoped Select All, rich Preview copying, selection-anchored comments, and threaded replies.
- Markdown rendering: use CommonMark-style Markdown, GitHub-Flavored Markdown (GFM), tables, task lists, alerts, footnotes, definition lists, syntax highlighting, sanitized HTML, and MathJax. Preview Styling controls the code theme, math font, Mermaid theme and style, and supported emoji skin tone.
- Document Outline: use the book-text button after Emoji, Find & Replace, and Full Screen to open a resizable right sidebar with collapsible heading branches, a Collapse/Expand All control, and section navigation in Editor, Preview, and Split modes. Copy a GitHub-compatible Markdown TOC with configurable heading depth, bulleted/numbered links or plain text, optional level normalization, and a collapsible wrapper. The outline follows the current document and shares Find & Replace's width and header styling.
- Localized discovery: open any of 15 language URLs with translated initial content and a localized starter document before JavaScript runs; changing the interface language preserves user-authored Markdown and Preview typography.
- Visual content: render Mermaid, PlantUML, Graphviz/DOT, D2, Vega-Lite, WaveDrom, Markmap, GeoJSON, TopoJSON, STL, and ABC notation.
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Import and export: open local files or GitHub content from branches, tags, commit SHAs, and optionally private repositories; export Markdown, standalone HTML, PNG, Standard PDF/Save as PDF, or Rendered PDF with remembered Light or Dark appearance and complete rich-content preparation for PDF and PNG.
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Optional sharing: create a Share Snapshot with View only or Can edit access, or start a temporary Live Share room with host, Can edit, and View only capabilities.
- Multiple delivery options: use the hosted web app, install the PWA, self-host static files, run Docker, deploy on Cloudflare, or build the Neutralino desktop application.
For verified behavior, limits, and implementation notes, read the feature reference.
Quick Start
Use the hosted application at markdownviewer.pages.dev, or run the repository through a local HTTP server:
git clone https://github.com/ThisIs-Developer/Markdown-Viewer.git
cd Markdown-Viewer
python -m http.server 8080
Open http://localhost:8080. Do not rely on file://; browser security rules can block Web Workers and Service Workers.
Other options:
Local and Network Behavior
Markdown Viewer is local-first, not network-free. The following table shows the main boundary:
| Workflow | Default data path |
|---|
| Editing, local imports, Preview, Workspace autosave, and most exports | On the device |
| Web libraries and uncached renderer dependencies | CDN requests in the web/PWA build |
| GitHub import and emoji lookup | Public content uses GitHub APIs and raw-content hosts; private content uses an optional PAT only with api.github.com |
| PlantUML, D2, Graphviz, Vega-Lite, WaveDrom, and some diagram previews | Diagram source can be sent to PlantUML, Kroki, or mermaid.ink |
| Consented image, GIF, and video insertion | Public, content-addressed Cloudflare media storage for 90 days |
| Large Share Snapshot | Cloudflare KV for 90 days |
| Live Share | WebSocket relay through a Cloudflare Durable Object; document content is not persisted server-side |
| External images, media, links, and map tiles | The referenced external host |
Share Snapshot and Live Share URLs are bearer links. Anyone who obtains a valid link and capability can use the access it grants. Live Share is not end-to-end encrypted. See Privacy and Security before using network features with sensitive content.
Visual Renderer Summary
| Fence | Rendering path |
|---|
mermaid | Client-side; insertion previews can use mermaid.ink or Kroki |
plantuml | PlantUML server; Kroki fallback |
d2, graphviz, dot, vega-lite, vegalite, wavedrom | Kroki |
markmap | Client-side Markmap and D3 |
geojson, topojson | Client-side Leaflet; map tiles can use the network |
stl | Client-side Three.js/WebGL |
abc | Client-side ABCJS; playback needs browser audio support |
math and LaTeX delimiters | Client-side MathJax |
Remote renderer services receive the source of the diagram they render. Do not send sensitive diagram source unless you trust the configured service. See the Markdown Reference for syntax and the feature reference for limitations.
Documentation
Important Limits
- Workspace backup import does not merge workspaces; it permanently replaces the current workspace after confirmation.
- Workspace backups do not include trash, desktop history, or crash-recovery journals.
- Recognized Trash records are permanently removed after 30 days; corrupt, incomplete, or future-format records remain for manual review.
- A local Markdown file larger than 10 MB is rejected.
- The GitHub credential vault stores up to 50 named PAT entries; each token name is limited to 60 characters.
- Managed source media is limited to 25 MiB before processing; stored payload limits are 300 KiB for still images, 5 MiB for GIFs, and 10 MiB for videos.
- Stored Share Snapshot content is limited to 8,000,000 characters and expires after 90 days.
- Live Share allows up to 64 WebSocket participants and 8 MB per live message.
- STL source is limited to 2 MiB and rendered geometry to 300,000 vertices.
- The desktop vault retains up to 20 recent history copies per document.
- Desktop linked-folder scans are bounded to 10,000 Markdown files, 40,000 entries, 2,000 directories, 32 levels, 20 MiB per source, 200 MiB staged content, and 60 seconds. Recovery drafts are not independent backups, and native filesystem checks cannot eliminate every race with another program.
- Raster PDF and PNG exports remain subject to browser memory, canvas, and cross-origin resource limits.
See Features: Known Technical Limits for context.
Showcase Projects
The following community project builds on Markdown Viewer and is maintained independently:
- Markdown Desk: A native macOS wrapper built with Tauri that adds native file dialogs and handlers, menu-bar integration, automatic reloads, and in-app updates.
Development Journey
Markdown Viewer started as a small personal project on a PC: a simple Markdown viewer built with curiosity, mistakes, fixes, and a lot of care. The original version is still online and remains at the heart of the project.
Read the Development Journey for the longer project history.
Contributors
Markdown Viewer grows through contributions from its community.
Contributing and Support
See the contributing guide, Code of Conduct, and Security Policy. The issue tracker is available for bugs and feature requests.
License
Markdown Viewer is licensed under the Apache License 2.0.
