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Feature checklists make every tool look equivalent. This table leads with the three things that actually differ — what it costs you before it works, whether your files leave your device, and where the free version stops.
| diagrams.netdiagrams.net | Lucidchartlucidchart.com | PlantUML Online Serverplantuml.com | Mermaid Live Editormermaid.live | |
|---|---|---|---|---|
| What it does | Full diagram editor that works without an account or a saved file | Polished diagramming with real-time collaboration and smart layout | Renders UML from a text description, with the source encoded in the URL | Write a diagram as text and watch it render beside you |
| What it costs you | No sign-upWorks the moment the page loads. No account, no email, no trial. | Free tierA genuinely usable free tier with paid plans for volume or team features. | No sign-upWorks the moment the page loads. No account, no email, no trial. | No sign-upWorks the moment the page loads. No account, no email, no trial. |
| Your files | Runs on your device | Runs on their server | Runs on their server | Runs on your device |
| Where it stops | No automatic layout — a fifty-box diagram is fifty boxes you positioned yourself. | Free accounts get three editable documents with a 60-object cap each, and lines count as objects. | Diagram source is sent to a public server to render, and the default styling looks its age. | Layout is decided by the renderer — if it routes an edge badly there is no way to drag it. |
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| Category | Diagrams & Whiteboards | Diagrams & Whiteboards | Diagrams & Whiteboards | Diagrams & Whiteboards |
| Last checked | 2026-07-29 | 2026-07-29 | 2026-07-29 | 2026-07-29 |
| Open the site | Open | Open | Open | Open |
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