# D2 — Modern Diagram Scripting Language

> A declarative language that turns text into diagrams, supporting sequence diagrams, flowcharts, and more with automatic layout.

## Install

Save as a script file and run:

# D2 — Modern Diagram Scripting Language

## Quick Use
```bash
# Install via script
curl -fsSL https://d2lang.com/install.sh | sh -s --
# Or via Homebrew
brew install d2

# Create a diagram
echo 'x -> y -> z' > example.d2
d2 example.d2 example.svg
```

## Introduction
D2 is a modern diagram scripting language developed by Terrastruct that compiles text to diagrams. It provides a readable, declarative syntax for creating architecture diagrams, flowcharts, sequence diagrams, and more, with automatic layout powered by multiple engines.

## What D2 Does
- Compiles human-readable text definitions into SVG, PNG, and PDF diagram outputs
- Supports sequence diagrams, flowcharts, entity-relationship diagrams, and class diagrams
- Provides multiple layout engines including dagre, ELK, and TALA for automatic arrangement
- Enables theming, styling, and interactive tooltips on generated diagrams
- Offers a watch mode that live-reloads diagrams in the browser as you edit

## Architecture Overview
D2 is written in Go with a pipeline architecture: the parser converts D2 text into an abstract syntax graph, the compiler resolves references and connections, a layout engine positions nodes, and the renderer emits the final SVG or image. Layout engines are pluggable, allowing users to choose between the open-source dagre/ELK backends or the proprietary TALA engine for advanced layouts.

## Self-Hosting & Configuration
- Install the d2 binary on Linux, macOS, or Windows via the official install script or package managers
- Run `d2 --watch input.d2 output.svg` for a live-reloading development workflow
- Configure default theme, layout engine, and output format via CLI flags or a d2 config file
- Integrate into CI pipelines to auto-generate documentation diagrams on every commit
- Use the D2 Playground (TALA-powered) for browser-based editing without local installation

## Key Features
- Readable syntax with minimal boilerplate compared to DOT or Mermaid
- First-class support for sequence diagrams with actors, spans, and notes
- Built-in themes (including dark mode) and extensive styling options via D2 style blocks
- Composable imports allow splitting large diagrams across multiple files
- CLI-first design with watch mode, making it easy to embed in dev workflows

## Comparison with Similar Tools
- **Mermaid** — browser-native and widely embedded in Markdown renderers, but less expressive layout control
- **PlantUML** — mature UML-centric tool with Java dependency; D2 is a single Go binary
- **Graphviz (DOT)** — powerful graph layout but archaic syntax; D2 offers a modern developer experience
- **Excalidraw** — hand-drawn style visual editor; D2 is text-first and version-control friendly
- **Structurizr** — focuses on C4 architecture models; D2 is general-purpose diagramming

## FAQ
**Q: Is D2 free and open source?**
A: Yes, D2 is open source under the MPL-2.0 license. The TALA layout engine is proprietary but optional.

**Q: Can I use D2 in my documentation pipeline?**
A: Absolutely. D2 integrates with CI/CD systems and supports output to SVG, PNG, and PDF formats.

**Q: Does D2 support dark mode?**
A: Yes, D2 ships with multiple built-in themes including several dark mode variants.

**Q: How does D2 compare to Mermaid for Markdown docs?**
A: D2 offers more layout control and diagram types, while Mermaid has broader native Markdown rendering support.

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

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Source: https://tokrepo.com/en/workflows/asset-48d4cd59
Author: Script Depot