Mermaid vs PlantUML vs Draw.io: Which Diagram Tool Actually Fits Your Workflow?

So you need to document some architecture, and now you're stuck deciding between Mermaid, PlantUML, and Draw.io. I've used all three over the past few years, and here's the honest breakdown.

The Short Answer

Mermaid if you want simplicity and native Markdown support. PlantUML if you need complex UML diagrams with serious customization. Draw.io if your team prefers visual drag-and-drop editing.

But the real answer depends on how you actually work.

Mermaid: The Markdown-First Choice

Mermaid is what happens when someone says "what if diagrams worked like Markdown?" You write text, and diagrams appear. That's it.

Here's a flowchart:

graph TD
    A[Start] --> B{Check Config}
    B -->|Valid| C[Deploy]
    B -->|Invalid| D[Error]

The killer feature? GitHub, GitLab, Notion, and dozens of other platforms render Mermaid natively. No plugins, no export steps. Write it in your README, and it just shows up.

Where it shines:

• Quick documentation alongside code
• Sequence diagrams for API flows
• Flowcharts and state diagrams
• Teams that live in Markdown

Where it struggles:

• Complex C4 architecture diagrams (support is still experimental)
• Heavy customization needs
• Mind maps (not supported at all)

The syntax is intuitive enough that you'll pick it up in an afternoon. The trade-off is less control over exactly how things look.

PlantUML: Power User Territory

PlantUML has been around forever. It's battle-tested, deeply customizable, and supports almost every diagram type you can think of.

The catch? It requires Java to run, which adds setup friction. And the syntax, while powerful, is more verbose:

@startuml
actor User
participant "Web Server" as WS
database "Database" as DB
User -> WS: Request
WS -> DB: Query
DB --> WS: Results
WS --> User: Response
@enduml

Where it shines:

• Complex UML diagrams with precise control
• C4 architecture models (solid support with sprites)
• Mind maps and work breakdown structures
• When you need every detail exactly right

Where it struggles:

• Initial setup (Java dependency)
• Steeper learning curve
• Rendered output can look dated without tweaking

PlantUML gives you more rope - which is great if you know what you're doing, less so if you just want a quick diagram.

Draw.io: The Visual Editor

Draw.io is fundamentally different. It's a visual editor where you drag boxes and connect them with arrows. No code, no syntax.

Where it shines:

• Non-technical team members can contribute
• Complex custom graphics and layouts
• When you need pixel-perfect positioning
• Floor plans, infographics, wireframes

Where it struggles:

• Version control (it's XML, not human-readable diffs)
• Automation and CI/CD integration
• Keeping diagrams in sync with code changes

Draw.io is free, works in browsers, and exports to almost any format. But if your documentation lives in Git alongside code, the lack of text-based diffs becomes painful fast.

The Real Comparison

| What You Need | Best Pick |
|---------------|-----------|
| Quick docs in Markdown | Mermaid |
| Complex UML with control | PlantUML |
| Non-technical contributors | Draw.io |
| Version control friendly | Mermaid or PlantUML |
| Pixel-perfect layouts | Draw.io |
| Fastest to learn | Mermaid |
| Most diagram types | PlantUML |

What I Actually Use

Honestly? Mermaid for 80% of what I do. Sequence diagrams in PRs, flowcharts in READMEs, quick architecture sketches. The GitHub integration alone makes it worth learning.

When I need complex C4 models or detailed class hierarchies, I reach for PlantUML. The extra setup pays off when you're building something that needs to communicate intricate relationships.

Draw.io comes out when I'm working with designers or product folks who don't want to learn syntax. It's the right tool when collaboration matters more than version control.

One Thing to Know in 2025

PlantUML support in Draw.io is being deprecated at the end of 2025. If you've been using both together, you'll need to plan a migration. Mermaid integration remains supported.

Making the Choice

Skip the analysis paralysis. If you're reading this on a documentation site, you probably care about version control and developer workflows. That means Mermaid or PlantUML.

Start with Mermaid. It has the gentlest learning curve and the broadest platform support. You can always graduate to PlantUML later when you hit its limits - and you'll know exactly why you need the extra power.

The best diagram tool is the one your team actually uses. A simple Mermaid flowchart in your README is infinitely more valuable than a perfect PlantUML diagram nobody maintains.

References

Mermaid Official Documentation - Complete syntax reference and examples

PlantUML Language Reference - Comprehensive guide to PlantUML syntax

Draw.io Blog: PlantUML to Mermaid Migration - Official migration guide

Dan Does Code: PlantUML vs Mermaid - Detailed syntax comparison

Gleek.io: Mermaid vs PlantUML - Feature-by-feature analysis