OnUML
OnUML: A low-cost web editor for AI-generated diagrams across four diagram formats. Ranked #14 of 32 in AI Diagram Generators by our editors (8.0/10); pricing: Free plan; best for low-cost multi-format diagram authors.
At a glance
- Editor score8.0 / 10
- PricingFree plan
- Best forLow-cost multi-format diagram authors
- Free planYes
- Paid from$4/mo
- Mermaid supportYes
- Facts checked20 Sep 2026
Where it wins
- Generates diagrams from natural-language prompts and supported image inputs
- Supports Mermaid, PlantUML, Draw.io, and mind-map editing modes
- Includes code repair, version history, sharing links, and PNG or SVG export
Where it doesn't
- Web-only access limits platform choice
- Free projects are limited to 2 diagrams per project
- The Free plan includes 10 model requests per day
Our verdict on OnUML
OnUML is a browser-based AI diagram generator and editor for people who work across Mermaid, PlantUML, Draw.io, and mind maps. It accepts natural-language prompts and supported image inputs, then combines code editing, visual editing, and live previews in one workspace. Project organization, cloud saving, version history for diagram code, shareable links, and PNG or SVG export make it suited to authors who need to create, revise, and distribute diagrams rather than generate a single draft.
The pricing structure starts with a Free plan that includes core editor access, 2 diagrams per project, 10 cloud projects per workspace, 2 workspaces, and 10 free model requests per day. The published plans show a Pro option at $4 per month with image upload, expanded project capacity, unlimited cloud projects per workspace, unlimited workspaces, and no daily limit on free model requests. A second Pro entry at $8 per month adds 500 monthly included credits. One-time AI credit packs are also available: $4.9 for 240 credits, $9.9 for 500 credits, or $19.9 for 1,100 credits.
OnUML’s main strength is breadth within a focused diagram workflow. Users can move between supported diagram modes, repair diagram code with one click, preview changes live, and retain version history as projects evolve. Its web-only delivery keeps the access model straightforward, while the Free plan provides a way to work within defined project, workspace, and request limits. Choose OnUML if low monthly cost, AI-assisted creation, and multi-format editing are priorities. Consider another option if native desktop access or diagram formats beyond Mermaid, PlantUML, Draw.io, and mind maps are essential.
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OnUML pricing
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OnUML fact sheet
| Free plan | Yes |
|---|---|
| Paid from | $4/mo |
| AI diagram limit | Not verified |
| Mermaid support | Yes |
| Real-time collaboration | Not verified |
| Diagram import | Not verified |
| Platform | Web |
| Export formats | PNG, SVG |
| Deployment | Cloud |
| Platforms | Web |
| Support | |
| Built for | Solo, Small business (editorial estimate) |
| Pricing | Free plan (source) |
| Website | onuml.com |
| Facts checked | 20 Sep 2026 |
Alternatives to OnUML
- OpenFlowKitA flexible free diagramming workspace for technical teams that prefer editable, portable outputs.9.4
- EraserA broad diagram workspace combining AI, diagram-as-code, collaboration, and integrations.9.3
- ArchwayA broad architecture diagram generator with AI input, collaboration, APIs, and self-hosting.9.2
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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
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