OnUML

About OnUML

OnUML is a browser workspace that generates and edits diagrams across three formats that usually live in three separate tools: Mermaid, PlantUML, and Draw.io. You supply text or an image as the source and AI drafts the diagram, then you refine it either through further prompts or by editing the underlying code, with the render updating in real time so code and picture stay in view together. The format split is treated as a deliberate choice rather than a detail — Mermaid for lightweight documentation-driven diagrams, PlantUML for formal UML and technical modelling, and Draw.io flows for visual architecture and whiteboard-style planning with drag, drop, connect, and resize on the canvas and a rich built-in shape library. Two things push it past being a thin wrapper. First, it supports a proper mind-map diagram type built for structured thinking rather than relying on the cramped mind-map syntax inside PlantUML or Mermaid, and mind-map nodes can be added and moved directly on the page without going back to code. Second, there is one-click AI repair for broken diagram code: paste PlantUML or Mermaid that fails to render and it fixes the syntax so you can continue instead of hand-debugging. Everything exports from the same workspace, and the tool is usable free with no registration.

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