Free viewer for Markdown, Mermaid and JSON files: folder tree, search, TOC, math, diagrams, collapsible JSON, dark mode. • Opens .md files from your computer or the web, plus .mmd / .mermaid diagrams • Open a folder and switch files from the sidebar • Ctrl+K to search every file in the folder • Table of contents, light / dark theme • Code highlighting, math, Mermaid diagrams, task lists, alerts • Auto refresh while you edit