mermaid-cli is a command-line interface for generating diagrams from Mermaid syntax. It processes input files (.mmd, .md, .markdown) containing Mermaid diagram definitions and outputs SVG, PNG, or PDF files. The architecture centers around a Puppeteer-driven rendering pipeline that launches a headless browser to render Mermaid diagrams via the Mermaid library. Key features include Markdown diagram extraction, configurable theming, CSS injection, icon pack support, and programmable Node.js API. The CLI entry point is src/cli.js, which delegates to the run() and renderMermaid() functions in src/index.js for core functionality. External dependencies include Puppeteer, Mermaid, and various layout engines (ELK, tidy-tree).