D2 is a concise scripting language that lets you generate diagrams directly from plain text. It focuses on simplicity and readability, making it easy to embed visualizations in documentation and codebases. Designed for self‑hosted environments, D2 runs in the browser and can be integrated into CI pipelines, providing free, on‑premise diagram generation without vendor lock‑in.
Mermaid is a simple markdown-like script language for generating diagrams and flowcharts from text. It can be used to create a variety of diagrams, including flowcharts, sequence diagrams, and Gantt charts. Mermaid is often used in documentation and can be integrated into various tools and platforms.
- Zero cost, fully free
- Self‑hosted for full data control
- Simple, readable syntax reduces learning curve
- Integrates easily with CI pipelines and GitHub
- Easy to use
- Customizable
- Cross-platform
- Free
- Limited to 2D diagram types
- No native desktop application, relies on web UI or CLI
- Advanced styling requires manual configuration
- Limited features compared to other diagramming tools
- Steep learning curve for complex diagrams
- Limited support for collaboration
More alternatives & similar tools
Alternatives to d2
View all →Alternatives to Mermaid
View all →The Verdict
AI-generated from listing dataBoth Mermaid and d2 are free, open‑source text‑to‑diagram tools for developers, but Mermaid offers broader diagram types and richer theme customization, while d2 excels at simple syntax, CI/CD integration, and self‑hosting control.
Key differences
- •Mermaid supports more diagram types (flowcharts, sequence, Gantt) versus d2’s 2D focus (flowcharts, mind maps, ER).
- •d2 provides built‑in CI/CD and GitHub Actions integration; Mermaid’s integrations are limited to source‑code platforms (GitHub, GitLab, Bitbucket).
- •Mermaid offers live preview within many editors and multiple output formats (SVG, PNG); d2 relies on web UI or CLI for preview/export.
- •d2 can be self‑hosted for data privacy; Mermaid is primarily used as a library/service without self‑hosting guarantee.
- •Mermaid’s theming is more customizable via built‑in styles; d2’s advanced styling requires manual configuration.
Pricing & value
Both are free and open source, offering zero licensing cost.
Ease of use / learning curve
d2’s clear markdown‑like syntax is described as simple, reducing learning curve versus Mermaid’s steeper curve for complex diagrams.
Features & depth
Mermaid supports a wider range of diagram types (flowcharts, sequence, Gantt) and richer theme customization.
Integrations & ecosystem
Mermaid lists key integrations with GitHub, GitLab, Bitbucket; d2 focuses on CI/CD and GitHub Actions only.
Collaboration
Mermaid’s integration with popular code hosts facilitates collaborative editing; d2 lacks native collaboration features.
Scalability
d2’s self‑hosted deployment and CLI enable scaling in CI pipelines and internal documentation workflows.
Support
Both provide email and GitHub Issues as support channels.
Choose d2 if…
Organizations prioritizing simple syntax, CI/CD automation, and self‑hosted control over diagram generation.
Choose Mermaid if…
Teams needing diverse diagram types, richer styling, and tight integration with code repositories.
Common questions
Is there any cost to use either tool?
Both Mermaid and d2 are free and open source.
Can I host the tool on my own servers?
d2 supports self‑hosting; Mermaid does not specify self‑hosting capability.
Which tool offers more diagram variety out of the box?
Mermaid supports flowcharts, sequence diagrams, and Gantt charts, providing broader variety than d2’s 2D diagrams.