readmd 0.5.1

readmd — terminal Markdown viewer

A terminal-first, feature-rich Markdown viewer with an optional browser mode. It renders Markdown right in your terminal — including mermaid and D2 diagrams (as real images via Sixel), syntax-highlighted code, tables, GitHub-style alerts, math, and an Azure DevOps [[_TOC_]] table of contents — and live-reloads as you edit. When you want full fidelity, the same document opens in your browser with one keypress.

dnx readmd report.md                 # view in the terminal (TUI)
dnx readmd report.md --browser       # view in the browser (full fidelity)

Requires the .NET 10 SDK (for dnx). d2 on your PATH is needed for D2 diagrams. For mermaid, readmd uses a local mmdc (mermaid-cli) if it's installed; otherwise it downloads a headless browser automatically on first use.

Features

• Runs in the terminal as a full TUI (alternate screen, scrolling, overlays).
• One-shot launch via dnx readmd <file> (or npx-style global install).
• GitHub-Flavored Markdown: headings, bold/italic/strikethrough, inline code, links, tables, lists, blockquotes, hard breaks, emoji shortcodes.
• GitHub alerts ([!NOTE], [!TIP], [!IMPORTANT], [!WARNING], [!CAUTION]) with colored icons and titles.
• Task lists (- [x] / - [ ]) rendered as ☑ / ☐, footnotes with linked markers, and definition lists.
• Tables honor column alignment (left/center/right) and wrap wide cells instead of truncating; long URLs wrap rather than clipping.
• YAML front matter is recognized and used for document metadata: the title sets the document/window title, and title/author/date/tags render as a compact header (the raw block never leaks into the body).
• Live reload on file change. The browser preserves scroll position (DOM-morphing instead of full reload); the terminal repaints in place and caches diagrams so they don't flicker.
• Search & navigation: / to search, n/N to jump, t for a table-of-contents overlay, ? for keybindings.
• Azure DevOps [[_TOC_]] marker support, plus a sticky TOC sidebar in the browser.
• Diagrams from fenced code blocks: mermaid, D2, Graphviz (graphviz/dot), and PlantUML (plantuml/puml) — rendered to images inline in the terminal (via Sixel) and shown natively in the browser. Render failures are reported inline with an actionable message.
• Math via KaTeX (browser) / a Unicode approximation (terminal), code via TextMate (terminal) / highlight.js (browser).
• Multi-file wiki navigation: follow local .md links with back/forward history (sandboxed to the document's directory). Opening an external link asks for confirmation first.
• Browser mode (--browser) for pixel-perfect rendering, served locally (loopback only) from an embedded web server. The browser view adds: export the current document to a self-contained .html or a .pdf; copy buttons on code blocks and permalink anchors on headings; a diagram lightbox (click any mermaid/D2 diagram to zoom/pan, copy or open its SVG); project-wide search across the wiki and a Ctrl+P quick-open file palette; and persisted theme/zen/sidebar preferences.
• Export & piping: --export writes a self-contained .html or .pdf; with a redirected stdout (or stdin via -) it renders to text, so readmd file.md | less -R and cat file.md | readmd - just work.

Usage

readmd <file> [options]
readmd -            # read Markdown from standard input

Options:
  -b, --browser        Open in the browser instead of the terminal.
  -p, --port <port>    Port for browser mode (0 = pick a free port; 0–65535).
      --no-open        In browser mode, start the server but don't launch a browser.
      --best-effort    Terminal mode: skip the headless-browser download; mermaid
                       diagrams open in the browser instead of rendering inline.
  -e, --export <path>  Export to a self-contained file and exit; format from the
        (-o)           extension: .html (single file, assets inlined) or .pdf.
      --print          Render to stdout and exit (plain text, or ANSI on a TTY).
                       Implied when stdout is a pipe/file, or when reading stdin.
      --theme <theme>  Color theme: dark, light, or auto (auto honors COLORFGBG,
                       else defaults to dark).
      --background <b>  'solid' paints a solid themed background (overrides terminal
       (--bg)          transparency, like OpenCode); 'terminal' shows the terminal
                       background through. Toggle live with ].
      --d2-path <p>    Explicit path to the d2 executable.
  -v, --version        Print the version and exit.
  -h, --help           Show help.

Export & piping

readmd is pipeline-friendly. When stdout is redirected (or you read from stdin), it renders to text instead of starting the interactive UI:

readmd report.md | less -R              # paged, ANSI-colored when the pager is a TTY
readmd report.md > report.txt           # plain text (styles stripped)
cat report.md | readmd -                # render from stdin
readmd report.md --export report.html   # one self-contained HTML file (assets inlined)
readmd report.md --export report.pdf    # PDF (rendered via the bundled headless browser)

Exported HTML is fully standalone: CSS, JavaScript and KaTeX fonts are inlined, local images become data URIs, D2 diagrams are pre-rendered to inline SVG, and mermaid/KaTeX run client-side from the embedded libraries — so the file opens anywhere with no server. PDF export reuses that HTML through the same headless Chromium that renders mermaid.

Terminal keybindings

Vim-style motions are supported throughout, plus the mouse wheel scrolls.

On Windows, mouse-wheel scrolling captures the mouse, which disables the terminal's native click-drag text selection. Press m to enter mark mode (the status bar shows [SELECT]): drag with the left button to select text, then right-click to copy the selection to the clipboard. Esc clears the selection; press m again to leave mark mode and restore wheel scrolling. On macOS/Linux the mouse is always reported (SGR), so drag-select and right-click-copy work directly. Copy uses the Win32 clipboard on Windows and OSC 52 elsewhere (Windows Terminal, WezTerm, kitty, iTerm2, …).

Theme and background can also be set at launch with --theme and --background.

Browser keybindings

The browser view uses the same vim-style motions, plus toggles to hide chrome:

Configuration

readmd reads an optional JSON config so you don't have to repeat flags, and can define custom color themes and remap keys. It looks for a user-level file — ~/.config/readmd/config.json (honoring XDG_CONFIG_HOME) on macOS/Linux, or %APPDATA%\readmd\config.json on Windows — and a project-level .readmd.json found by walking up from the document's directory. Project settings override user settings; command-line flags override both. A missing or malformed file is ignored.

{
  // Defaults used when the matching flag isn't passed:
  "theme": "nord",            // "dark" | "light" | "auto" | a custom theme name below
  "background": "solid",      // "solid" | "terminal"
  "d2Path": "/usr/local/bin/d2",
  "graphics": "auto",         // "sixel" | "half-block" | "none" | "auto" (inline image mode)

  // Custom terminal color themes (any omitted color falls back to the dark/light base):
  "themes": {
    "nord": {
      "dark": true,
      "text": "#d8dee9", "background": "#2e3440", "backgroundElevated": "#3b4252",
      "h1": "#88c0d0", "h2": "#81a1c1", "h3": "#8fbcbb",
      "link": "#5e81ac", "accent": "#b48ead", "rule": "#434c5e"
    }
  },

  // Remap the common single-key actions (others keep their defaults):
  "keys": {
    "quit": "x",
    "search": "s",
    "pagedown": "space"
  }
}

Remappable actions: quit, scrollDown, scrollUp, pageDown, pageUp, goBottom, search, searchNext, searchPrev, toc, openInBrowser, selectionMode, rerender, toggleTheme, toggleBackground, help. (Arrows, mouse, Ctrl-combinations, the gg prefix, and 1–9 link-following are fixed.)

Shell completions & man page

readmd can print completion scripts for bash, zsh, fish, and PowerShell, plus a man page:

# bash / zsh (load now, or add the line to your rc file)
source <(readmd completions bash)
source <(readmd completions zsh)

# fish
readmd completions fish > ~/.config/fish/completions/readmd.fish

# PowerShell (add to $PROFILE)
readmd completions pwsh | Out-String | Invoke-Expression

# man page
readmd man > ~/.local/share/man/man1/readmd.1

How it works

readmd is a single .NET 10 tool composed of five projects:

The Markdig pipeline and diagram cache are shared by both front-ends, so the terminal and browser views stay consistent and diagrams are only rendered once per content hash.

Terminal image support

Inline diagrams and images in the terminal use the Sixel graphics protocol where available (Windows Terminal ≥ 1.22, WezTerm, xterm, mintty, foot, …). On terminals without Sixel, readmd automatically falls back to Unicode half-block (▀) rendering, which works on any truecolor terminal (kitty, iTerm2, the Linux console, tmux, …) — diagrams and images still render inline, just at lower resolution. Force a mode with READMD_GRAPHICS=sixel|half-block|none (or "graphics" in config); none shows only the diagram caption. You can also run with --best-effort and press o to view diagrams in the browser.

Platform support

readmd targets .NET 10 and is cross-platform (Windows, macOS, Linux). Mouse support — wheel scrolling, click-to-follow-link, and drag-select in m mark mode — works on all three: Windows uses the console API, while macOS/Linux use SGR mouse reporting (with the terminal put in raw mode via termios). Every keybinding works on all platforms, and the browser front-end is identical everywhere.

Mermaid rendering: if a local mmdc (mermaid-cli, npm i -g @mermaid-js/mermaid-cli) is on your PATH — or set via mermaidCliPath in config — readmd uses it and skips its own browser download entirely. Otherwise the first mermaid diagram triggers a one-time headless-browser (Chromium) download via Playwright, which can be large; use --best-effort to skip it (mermaid then opens in your browser on demand). D2 requires the d2 binary on your PATH (or --d2-path); if it's missing, the diagram area shows an actionable message. Graphviz blocks require dot on your PATH, and PlantUML blocks require plantuml (and Java); both can also be pointed at via graphvizPath/plantUmlPath in config.

Building from source

git clone https://github.com/MoaidHathot/readmd
cd readmd
dotnet build Readmd.slnx
dotnet test tests/Readmd.Tests/Readmd.Tests.csproj                   # run the test suite
dotnet run --project src/Readmd.Cli -- samples/demo.md            # terminal
dotnet run --project src/Readmd.Cli -- samples/demo.md --browser  # browser

# Pack & install the tool locally
dotnet pack src/Readmd.Cli -c Release -o artifacts/nupkg
dotnet tool install --global --add-source artifacts/nupkg readmd

samples/demo.md exercises every feature (TOC, tables, task lists, alerts, code, mermaid, D2, math, multi-file links). CI (GitHub Actions) builds and tests on Windows, macOS, and Linux, and packs the tool.

tools/SixelView is a dev-only diagnostic that decodes the terminal's Sixel/ANSI output back to PNG for visual verification; it is not part of the shipped tool.

License

MIT