What is markmark?

MarkMark is a native macOS app for reading Markdown files, with a built-in workflow for annotating text and sending your notes to an AI for revision. Markdown is a plain-text format commonly used for documentation, notes, and content generated by AI tools. MarkMark renders those files so they look formatted, rather than showing the raw symbols. The app uses a three-pane layout: a file tree on the left, the rendered document in the middle, and an outline of headings on the right. You can open folders and browse files with keyboard navigation, open multiple files in separate windows, export to PDF, and switch between 33 visual themes. The main feature that sets it apart from a standard reader is annotation support using a format called CriticMarkup. While reading a rendered document, you can select any text and mark it for deletion, replacement, commenting, or highlighting. The annotations appear visually in the document, with deletions shown as red strikethrough and insertions in green, so you can see your feedback at a glance while reading. A single button in the title bar copies the full document with all annotations attached, plus a guiding prompt, ready to paste into any AI chat. The intended flow is: an AI produces a Markdown document, you open it in MarkMark, annotate the parts you want changed, copy everything, paste it back into the AI, and the AI revises based on your specific notes. Annotations use a plain-text standard, so they are portable and not tied to this app. A single click also removes all annotations and restores the original text. The app renders diagrams in Mermaid and PlantUML formats, supports math formulas through KaTeX, and highlights code blocks in more than 30 programming languages. It runs on macOS 15 and later, as a universal binary that works on both Intel and Apple Silicon Macs. The project is forked from an earlier Markdown reader and adds the annotation and AI-handoff workflow on top. It is released under the MIT license.