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nbs-md-viewer

Terminal-based markdown viewer. Reads markdown from stdin and renders it with full styling (colour, bold, italic, underline, box drawing) in the terminal. Read-only — navigate with keyboard, quit with q.

Usage

nbs-md-viewer < README.md
cat document.md | nbs-md-viewer
nbs-md-viewer --width=100 < document.md

What It Does

Parses markdown into an AST, renders it with styled display lines, and presents a scrollable pager in the terminal's alternate screen buffer. The terminal is fully restored on exit.

Supported Markdown

Element Syntax Rendering
Headings # through #### Coloured text, H1/H2 with background band
Paragraphs Plain text Reflowed to terminal width
Bold **text** Bold attribute
Italic *text* Italic + subtle background hint
Bold italic ***text*** Both attributes
Inline code `code` Green on dark background
Code fences ``` with optional language Bordered block with syntax highlighting
Tables GFM pipe tables Unicode box drawing with alignment
Lists - item or 1. item Bullets (•◦▪) or numbers, nested to 3 depths
Blockquotes > text Vertical bar with dimmed text
Links [text](url) Blue underlined text + dim URL
Horizontal rules --- Full-width line
Hard breaks Two trailing spaces Line break within paragraph

Syntax Highlighting

Code fences with a language tag are syntax-highlighted:

Language Tags
C c, h
C++ cpp, c++, cc, cxx, hpp
JavaScript js, javascript
TypeScript ts, typescript
Python py, python
Pascal / Honest pas, pascal, delphi, honest

Highlighting covers keywords, types, strings, numbers, comments, and preprocessor directives. Multi-line comments and strings maintain state across lines.

Key Bindings

Key Action
Up / Down Scroll one line
Page Up / Down Scroll one page
Home Jump to top
End Jump to bottom
Left / Right Pan wide tables and code blocks
h / ? Help screen
q Quit

On Mac: use Fn + Arrow for Page Up/Down/Home/End.

Options

Option Default Description
--width=N auto-detected Override terminal width (useful when PTY reports wrong size)

Architecture

Four-stage pipeline:

stdin → [Parser] → [AST] → [Renderer] → [Viewport] → terminal
  • Parser: Two-pass (block structure, then inline formatting)
  • AST: Immutable after construction, owned by document node
  • Renderer: Produces styled display lines with paragraph reflow
  • Viewport: Manages scrolling, horizontal panning, and terminal output

Dependencies

Uses existing nbs-framework modules:

  • nbs_term_attr — colour and style output (256-colour)
  • nbs_ts_wcwidth — character display width (CJK, emoji)
  • nbs_ts_bidi — bidirectional text reordering (RTL support)

No external libraries. Pure C, self-contained within nbs-framework.

Build

cd src/nbs-md-viewer
make            # build binary + tests
make install    # install to bin/
make test       # run unit tests
make asan       # build with AddressSanitizer

Terminal Requirements

Works on any terminal supporting:

  • 256-colour mode (SGR 38;5;N / 48;5;N)
  • Alternate screen buffer (DECSET 1049)
  • UTF-8 with Unicode box drawing characters

Tested on macOS Terminal.app and iTerm2. On Windows via SSH, terminal resize may not propagate — use --width=N as a workaround.