PlantUML & Mermaid diagrams.
Free. Private. In your browser.

16 diagram types. No account. No server. Export SVG, PNG, or source to disk.

Start Diagramming — Free
auth-flow.puml PlantUML
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PlantUML + Mermaid. 16 types. One editor.

Write in whichever syntax you prefer — SeedUML auto-detects and renders.

PlantUML

Mermaid

Text in, diagrams out

Never used diagram-as-code? Here's why teams are switching from drag-and-drop.

🤖

AI-native

Paste a sequence diagram into ChatGPT and say "add error handling." It works — because your diagram is text, not pixels. Try that with a PNG from a visual editor.

📈

Version-control friendly

Diagram source is plain text. It diffs, merges, and lives in your Git history alongside the code it documents. Review diagram changes in a pull request just like code.

⚡

Faster than dragging

No mouse, no palette, no alignment fiddling. Type A -> B: request and you have a sequence diagram. Modify 10 arrows in seconds, not minutes.

"Add error handling to this diagram" — any LLM can do this because it's just text
@startuml Client -> API: POST /order API -> DB: Insert order DB --> API: OK API --> Client: 201 Created @enduml

Your diagrams. Your files. Your disk.

Everything stays in your browser. Download exactly what you need.

Export anything

Download SVG, PNG (2x resolution), or source file (.puml / .mmd). Smart filenames with timestamps and diagram type.

100% private

No server, no cloud, no account, no tracking. Zero network requests during rendering. Nobody sees your diagram — not even us.

Works offline

The entire rendering engine runs in your browser as a self-contained JavaScript bundle. No internet needed after the page loads.

Using Jira? Get diagrams inline in your issues.

Same rendering engine, installed as a Jira plugin. Diagrams appear directly in issue descriptions — not hidden in a panel.

Learn more — SeedUML for Jira