Mermaid vs Graphviz: Which Diagram-as-Code Tool Fits Your Workflow?

Mermaid and Graphviz both generate diagrams from text, but they excel in different situations. Mermaid is great for fast documentation and human-readable diffs. Graphviz is great for large, algorithmic graphs where layout control and determinism matter.

Quick comparison

Feature	Mermaid	Graphviz
Syntax style	Declarative, Markdown-like	DOT language
Rendering engine	JavaScript (client or Node)	Native binaries and libraries
Best for	Docs, onboarding, quick diagrams	Complex graphs, infrastructure maps
Learning curve	Low	Moderate
Visual customization	High-level themes	Low-level attributes

Syntax side by side

Mermaid flowchart

graph TD
  Dev[Developer] --> CI[CI Pipeline]
  CI --> QA[Quality Checks]
  QA --> Prod[Production]

Graphviz DOT

digraph Delivery {
  rankdir=LR;
  Dev [label="Developer"];
  CI [label="CI Pipeline"];
  QA [label="Quality Checks"];
  Prod [label="Production"];

  Dev -> CI -> QA -> Prod;
}

What the syntax tells you

Mermaid is concise and readable, so it works well in docs and PRs.
Graphviz is explicit and configurable, so it works well for complex graphs where layout matters.

Styling and theming

Mermaid

Themes handle most styling decisions for you.
Great for consistent presentation across product docs.
Easy to tweak for quick, readable results.

Graphviz

Every node, edge, and graph attribute can be controlled.
Ideal for deterministic output in automated pipelines.
Better when you need precise placement and layout rules.

Performance and automation

Mermaid renders quickly in the browser, which keeps docs fast and interactive.
Graphviz renders well in headless environments, which is why it is common in CI pipelines that generate PDFs or SVGs.

Build pipeline fit

Use case	Mermaid	Graphviz
Markdown documentation	✅ Easy to embed	⚠️ Requires rendered image
Docs-as-code sites	✅ Plugins and MDX support	✅ CLI friendly
Infrastructure reports	✅ Good for storytelling	✅ Strong for network topology
Very large graphs	⚠️ Layout can slow down	✅ Built for scale

What teams notice in practice

Mermaid diagrams are faster to write and easier for non-engineers to review.
Graphviz shines when you need deterministic layouts or very large dependency graphs.
Teams often mix them: Mermaid for narrative docs, Graphviz for automated infrastructure diagrams.

Recommendation

Start with Mermaid if your diagrams are part of product storytelling, onboarding, or knowledge sharing. Choose Graphviz if you care about algorithmic layout control, large graph rendering, or automation in CI. UniDiagram supports both, so you can keep a single workflow even if your docs mix formats.

If your problem is inconsistent diagram output or an editor that slows you down, UniDiagram solves it with a better editor experience, live previews, and AI guidance. It helps you produce clean, shareable diagrams without the usual friction.