Mermaid is a mature, browser-oriented TypeScript monorepo that renders Markdown-like text definitions into SVG diagrams. In production it supports over 20 diagram families (flowchart, sequence, class, state, gantt, mindmap, pie, git, ER, C4, sankey, block, agentflow, and more), with a pipeline that detects diagram type from text, lazily loads a parser, builds a diagram-specific data model, and renders through a shared rendering-util layer. Parsing is split across Langium, Chevrotain, and legacy JISON grammars; layout is provided by dagre, ELK, a custom swimlane/orthogonal router, and tidy-tree plugins. The public API (initialize/run/parse/registerExternalDiagrams) makes this a plugin-extensible library rather than a standalone application, though it also ships a local editor, dev-explorer, and extensive e2e tooling. The codebase shows high engineering craft: CI is extensive with Vitest, Playwright visual regression, code coverage, security scanning, dependency automation, and changesets for versioning. Accessibility, XSS sanitization, and config validation are treated as first-class concerns. The theme system is particularly well-structured, managing multiple looks and color palettes through a centralized color-theme gate. The primary weaknesses are scale-driven: mixed parser ecosystems, a very large config surface, many beta diagram types, and highly intricate layout code that is expensive to change. It is neither a data-research repository nor a service; its research-like components are the layout algorithms and geometry validation, which remain embedded in a library architecture.

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).