Markdown Viewer for Eclipse

A Markdown editor for Eclipse with a preview tab. It renders GitHub Flavored Markdown with the same parser VS Code uses (markdown-it), draws Mermaid and PlantUML diagrams, keeps the source and the preview at the same scroll position, and exports a PDF in one click.

한국어 README

Dark theme	Light theme

Dark theme	Light theme (also used for PDF)

The screenshots show docs/sample.md with the default settings.

Features

Feature	Details
Tabs	Source and Preview tabs in one editor area, opening on Preview by default
Scroll sync	Switching tabs keeps the scrollbar position: at the bottom of one means at the bottom of the other
Rendering	GFM tables, task lists, syntax highlighting, heading anchors (table of contents links)
Mermaid	```mermaid blocks, with tighter default spacing and the preview's font
PlantUML	```plantuml / ```puml blocks, drawn locally by the bundled PlantUML, no server, no Graphviz
Images	PNG, GIF and SVG relative to the document, inline <svg>
Links	.md links open in Eclipse, web and mail links in the system browser
PDF export	A4, light colors, diagrams included
Font size	A- / A+ on the preview toolbar
Preferences	Fonts, line height, line breaks, dark and light colors (GitHub colors by default), diagram spacing
Offline	All JavaScript and PlantUML are inside the plugin JAR
Languages	English, Korean

The Source tab is Eclipse's Generic Editor, so TM4E syntax highlighting and the Wild Web Developer Markdown language server keep working.

Requirements

• Eclipse 2026-09 (4.41) or later with org.eclipse.ui.genericeditor (included in the Eclipse IDE packages)
• Windows 10 or 11 with Microsoft Edge (WebView2): everything, including the PDF export
• Linux: the preview works with WebKitGTK (libwebkit2gtk-4.1), checked on Ubuntu 24.04 under WSL; the PDF export does not (it uses Edge)

Install

Update site (Eclipse can then update it with Help > Check for Updates):

1. Help > Install New Software > Work with: https://insjang.github.io/eclipse-markdown-viewer/updates/ and press Enter.
2. Check Markdown Viewer, Next, accept the license, Finish. The plugin is not code-signed, so Eclipse asks whether to trust unsigned content: choose Trust Selected.
3. Restart Eclipse. .md files now open in the Markdown Viewer.

Or a single JAR, no p2:

1. Download io.github.insjang.mdviewer_<version>.jar from Releases.
2. Close Eclipse and copy the JAR into the dropins folder of your Eclipse installation.
3. Start Eclipse.

If .md files still open in another editor: right-click the file > Open With > Markdown Viewer, or set it as the default under Preferences > General > Editors > File Associations > *.md.

To uninstall: Help > About Eclipse IDE > Installation Details > Installed Software > Markdown Viewer > Uninstall, or delete the JAR from dropins, then restart Eclipse.

Build

JDK 21 or later and bash (WSL works).

ECLIPSE=/path/to/eclipse ./build.sh           # build/io.github.insjang.mdviewer_<version>.jar
ECLIPSE=/path/to/eclipse ./build.sh install   # also copy it into $ECLIPSE/dropins (close Eclipse first)
ECLIPSE=/path/to/eclipse ./build.sh site      # also build a p2 update site in build/site (feature/ holds feature.xml)

The first build downloads PlantUML (MIT build, 17 MB) from Maven Central and checks its SHA-1; it is not kept in git. Every build gets a new version qualifier, so a plain restart picks up a replaced JAR.

Preferences

Preferences > General > Editors > Markdown Viewer

Setting	Default
Body font	Malgun Gothic 11 pt
Code font	D2Coding ligature 10 pt (ligatures are turned off in the preview)
Line height	1.6
Theme	Dark
Keep line breaks as written	On (off: standard Markdown, lines join into one paragraph)
Open files on the Preview tab	On
Dark and light colors (13 each)	GitHub colors, Restore Defaults brings them back
Mermaid spacing: nodes, ranks, box padding	25, 30, 6 px (Mermaid's own defaults are 50, 50, 15)

• Indentation of lists, quotes and tabs in code is four characters of the code font.
• Diagrams use the body font and size; the PDF uses the light colors.
• A %%{init: {...}}%% line in a Mermaid block overrides the spacing for that diagram.

Security

Markdown from elsewhere can be opened safely.

• HTML in a document is sanitized with DOMPurify: scripts, event handlers and javascript: links are removed.
• Only http, https, mailto, document-relative paths and #anchors survive as URLs, and only http, https and mailto are handed to the operating system.
• Mermaid runs with securityLevel: 'strict'.
• PlantUML runs with its SANDBOX security profile: !include cannot read local files or URLs. Its SVG output is sanitized too.

Limitations

• PDF export is Windows only: the Edge path is fixed and the PDF is printed by headless Edge. macOS is untested.
• No outline view.
• PlantUML's built-in layout engine (smetana) ignores spacing settings; its default layout is already compact.

Source layout

src/io/github/insjang/mdviewer/
  MarkdownEditor.java          Source/Preview tabs, scroll sync, links, PDF export
  PlantUml.java                PlantUML blocks to SVG (font and colors, cache, sandbox)
  Activator.java               web assets, A-/A+
  PrefInit.java                preference defaults
  Colors.java                  colors per theme (GitHub defaults)
  MarkdownPreferencePage.java  preference page
  Contributor.java             undo, find and other editing actions
  Messages.java, messages*.properties   UI text (English, Korean)
web/
  preview.html / .js / .css    rendering, sanitizing, scrolling, styles
  *.min.js, hl-*.css           bundled libraries
feature/                       feature.xml, category.xml for the update site
icons/                         editor icon
test/
  check.js                     rendering (node)
  sanitize.js, plantuml.js     sanitizing and PlantUML wiring (node + jsdom)
  JsEscape.java, PlantUmlCheck.java

License

Developed with the help of AI coding assistants, including Claude (Anthropic).

Eclipse Public License 2.0. Bundled third-party libraries (markdown-it, markdown-it-task-lists, Mermaid, highlight.js, DOMPurify, PlantUML) keep their own licenses, listed in NOTICE.