# D2 — Declarative Diagram Scripting Language

> A modern diagram scripting language that turns text into diagrams, offering a readable syntax for architecture, flow, and sequence diagrams rendered from code.

## Install

Save in your project root:

# D2 — Declarative Diagram Scripting Language

## Quick Use
```bash
# Install via script
curl -fsSL https://d2lang.com/install.sh | sh -s --
# Create a diagram
echo 'x -> y -> z' > hello.d2
d2 hello.d2 hello.svg
```

## Introduction
D2 is a modern diagram scripting language that compiles text into diagrams. It provides a human-readable syntax purpose-built for software architecture, flowcharts, sequence diagrams, and entity-relationship models, allowing developers to version-control their diagrams alongside code.

## What D2 Does
- Compiles plain-text `.d2` files into SVG, PNG, or PDF diagrams
- Supports multiple diagram types: flowcharts, sequence diagrams, entity-relationship, and class diagrams
- Offers automatic layout via pluggable engines (dagre, ELK, TALA)
- Provides a watch mode that live-reloads diagrams in the browser on file save
- Handles nested containers, connections, icons, and theming natively

## Architecture Overview
D2 is written in Go and operates as a compiler pipeline. The parser reads `.d2` source into an AST, the compiler resolves references and connections, and a layout engine positions nodes and edges. The renderer then outputs the final image. Layout engines are pluggable: the open-source dagre and ELK engines ship by default, while the commercial TALA engine offers more advanced routing.

## Self-Hosting & Configuration
- Single binary install on Linux, macOS, and Windows with no runtime dependencies
- Also available via Homebrew, npm, and Docker
- Integrate into CI pipelines to auto-generate diagrams from source on every commit
- Theme customization through built-in themes or custom color overrides
- Use `d2 fmt` to auto-format `.d2` files for consistent team style

## Key Features
- Clean, readable syntax: `x -> y` defines a connection with minimal boilerplate
- Pluggable layout engines let you trade off speed for layout quality
- Watch mode with live browser reload for rapid diagram iteration
- Markdown and LaTeX support inside diagram labels
- Importable and composable: split large diagrams across multiple files with `...@file.d2`

## Comparison with Similar Tools
- **Mermaid** — embedded in Markdown renderers; D2 offers richer layout options and a standalone compiler
- **PlantUML** — Java-based with UML focus; D2 is a single Go binary with broader diagram types
- **Graphviz (DOT)** — venerable but minimal styling; D2 provides modern themes and nested containers
- **Excalidraw** — freehand drawing tool; D2 is text-to-diagram for version-controlled output

## FAQ
**Q: Can D2 diagrams be embedded in documentation sites?**
A: Yes. Generate SVGs at build time and embed them, or use community plugins for MkDocs, Docusaurus, and Hugo.

**Q: How does D2 compare to Mermaid for Git-based workflows?**
A: Both are text-to-diagram. D2 supports more layout engines, nested containers, and standalone CLI use, while Mermaid has broader native Markdown renderer support.

**Q: Is the TALA layout engine required?**
A: No. D2 ships with dagre and ELK (both open source). TALA is an optional commercial engine for advanced automatic layout.

**Q: Does D2 support dark mode?**
A: Yes. D2 includes multiple built-in themes including dark variants, selectable via the `--theme` flag.

## Sources
- https://github.com/terrastruct/d2
- https://d2lang.com/

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Source: https://tokrepo.com/en/workflows/eb65b8c4-431c-11f1-9bc6-00163e2b0d79
Author: AI Open Source