OnUML
What it is
OnUML is a web-based AI diagram generator and online UML editor for Mermaid, PlantUML, Draw.io, and mind maps. It creates diagrams from natural-language prompts and supported image inputs, then lets users edit visually or through code with a real-time preview. A one-click repair option addresses Mermaid and PlantUML syntax errors. Projects can hold multiple code versions, restore earlier content, and organize diagrams. PNG and SVG export and shareable links are supported. Its remote MCP server connects with Codex, Claude Code, Cursor, and OpenClaw, following signed-in workspace permissions. MCP can read and update Mermaid, PlantUML, and OnUML mind maps, but not Draw.io. Before changing a diagram, it checks for newer edits and stops if an overwrite would occur; retries aim to avoid duplicate creation. The free plan costs nothing, billed forever, with limits of two diagrams per project, ten cloud projects per workspace, two workspaces, and ten free model requests daily. Paid choices include $4.90 once, $8 monthly, $9.90 once, and $19.90 once plans.
For and against
For
- Generates diagrams from prompts and images
- Visual and code editing with live preview
- PNG and SVG export
- Version history and project organization
- MCP connections for listed coding agents
Against
- Free plan limits diagrams and projects
- Draw.io is excluded from MCP support
- Purchased credits expire after six months
- Image upload is not included in Free
The verdict
OnUML combines AI generation, UML editing, project history, and agent connectivity. Review the free quotas and credit expiration before choosing a paid option.
Who it suits
It suits people creating UML or other supported diagrams through prompts, code, or visual editing. Teams using supported coding agents may also use its MCP connection.
Plans and prices
Free
2 diagrams per project · 10 cloud projects per workspace · 2 workspaces · 10 free model requests per day
Read 9 Oct 2026 · onuml.com
Starter
240 credits · credits expire 6 months after issue
Read 9 Oct 2026 · onuml.com
Pro
500 monthly included credits · unlimited diagrams per project · unlimited cloud projects per workspace · unlimited workspaces
Read 9 Oct 2026 · onuml.com
Popular
500 credits · credits expire 6 months after issue
Read 9 Oct 2026 · onuml.com
Pro Pack
1,100 credits · credits expire 6 months after issue
Read 9 Oct 2026 · onuml.com
On the record
- AI repair
- The editor offers one-click repair for Mermaid and PlantUML syntax errors.onuml.com · read 9 Oct 2026
- Credit limits
- Purchased AI credits expire 6 months after issuance and do not unlock diagram, project, or workspace capacity.onuml.com · read 9 Oct 2026
- Editing
- Users can edit diagrams visually or through code and preview changes in real time.onuml.com · read 9 Oct 2026
- Export and sharing
- OnUML supports PNG and SVG export and shareable links.onuml.com · read 9 Oct 2026
- Generation
- It generates diagrams from natural-language prompts and supported image inputs.onuml.com · read 9 Oct 2026
- History and organization
- Users can save multiple code versions, restore earlier content, and organize diagrams by project.onuml.com · read 9 Oct 2026
- Integrations
- Its remote MCP server connects to coding agents including Codex, Claude Code, Cursor, and OpenClaw.onuml.com · read 9 Oct 2026
- MCP access
- The MCP server follows the signed-in account’s workspace permissions and supports reading and updating Mermaid, PlantUML, and OnUML mind maps; Draw.io is not supported through MCP.onuml.com · read 9 Oct 2026
- MCP safeguards
- OnUML says MCP updates check the latest diagram before changing it and stop if newer edits would be overwritten; retries are designed not to duplicate project or diagram creation.onuml.com · read 9 Oct 2026
- Operator
- The site says OnUML is a product operated by myun L.L.C.onuml.com · read 9 Oct 2026
- Product
- OnUML is an AI diagram generator and online UML editor for Mermaid, PlantUML, Draw.io, and mind maps.onuml.com · read 9 Oct 2026
- Support
- The site lists [email protected] as its contact email.onuml.com · read 9 Oct 2026
- Usage limits
- The free plan allows 2 diagrams per project, 10 cloud projects per workspace, 2 workspaces, and 10 free model requests per day.onuml.com · read 9 Oct 2026
