Heze

Headless Markdown and SVG previewer with deterministic PNG export.

Features · Installation · Quick start · CLI · Ruby API · Development

Heze is a headless Markdown and SVG previewer with deterministic PNG export. It keeps the parsed document tree independent from the renderer, then uses Zaniah for native previews and image output.

• GitHub Flavored Markdown — headings, lists, quotes, tables, fenced code, links, and images.
• Validated SVG input — unsupported filters, masks, text, and gradients fail before rendering.
• Deterministic PNGs — export the same document at an explicit width and height.
• Native preview — automatic macOS, Linux, and Windows backends with a textual fallback.
• Live reload — watch a document while editing, or browse a directory of Markdown files.
• Syntax highlighting — fenced code blocks are highlighted through Antares and Rouge.
• Encoding detection — UTF-8 BOM and Japanese Windows-31J input are handled safely.

gem install heze

Heze requires Ruby 3.2 or newer.

Open a native preview:

heze README.md

Export a deterministic PNG:

heze README.md --width 1200 --height 800 --export preview.png

Pass a directory to browse its Markdown files:

heze docs/

Usage: heze PATH [options]

Static SVG files use the same preview and export flow:

heze assets/mark.svg --export mark.png

Parse Markdown into an immutable document tree and render it directly:

require "heze"

document = Heze::Markdown.parse("# Hello\n\nRendered by Heze.")
png = Heze::Renderer.new(width: 1200, height: 630).render(document)
File.binwrite("preview.png", png)

bundle install
bundle exec rake
bundle exec rbs -I sig validate
gem build --strict heze.gemspec

Bug reports and pull requests are welcome on GitHub.

Heze is available under the MIT License.