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SPECIFICTION
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OnUML

onuml.com

From $8/mo Free plan WebAPI
Visit onuml.com
Spec score 7.7 #20 of 32 in AI Diagram Generators

What it is

OnUML is a web-based AI diagram generator and UML editor for Mermaid, PlantUML, Draw.io and mind maps. It creates diagrams from natural-language prompts and supported image inputs, then supports visual or code editing with a real-time preview. A one-click repair tool addresses Mermaid and PlantUML syntax errors. Users can save multiple code versions, restore earlier content and organize diagrams by project. PNG and SVG export and shareable links are supported. Its remote MCP server connects with coding agents including Codex, Claude Code, Cursor and OpenClaw. MCP follows workspace permissions and can read or update Mermaid, PlantUML and OnUML mind maps; Draw.io is excluded. It checks for newer edits before updates and stops if an overwrite would occur. The Free plan costs nothing, billed forever, with two diagrams per project, ten cloud projects per workspace, two workspaces and ten free model requests daily. Paid choices include 4.90 USD and 9.90 USD one-time plans, a 19.90 USD one-time Pro Pack and Pro at $8 a month.

Spec sheet

Product
OnUML is an AI diagram generator and online UML editor for Mermaid, PlantUML, Draw.io, and mind maps.Read 9 Oct 2026 · onuml.com
Integrations
Its remote MCP server connects to coding agents including Codex, Claude Code, Cursor, and OpenClaw.Read 9 Oct 2026 · onuml.com
Support
The site lists [email protected] as its contact email.Read 9 Oct 2026 · onuml.com
AI repair
The editor offers one-click repair for Mermaid and PlantUML syntax errors.Read 9 Oct 2026 · onuml.com
Credit limits
Purchased AI credits expire 6 months after issuance and do not unlock diagram, project, or workspace capacity.Read 9 Oct 2026 · onuml.com
Editing
Users can edit diagrams visually or through code and preview changes in real time.Read 9 Oct 2026 · onuml.com
Export and sharing
OnUML supports PNG and SVG export and shareable links.Read 9 Oct 2026 · onuml.com
Generation
It generates diagrams from natural-language prompts and supported image inputs.Read 9 Oct 2026 · onuml.com
History and organization
Users can save multiple code versions, restore earlier content, and organize diagrams by project.Read 9 Oct 2026 · onuml.com
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.Read 9 Oct 2026 · onuml.com
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.Read 9 Oct 2026 · onuml.com
Operator
The site says OnUML is a product operated by myun L.L.C.Read 9 Oct 2026 · onuml.com
Usage limits
The free plan allows 2 diagrams per project, 10 cloud projects per workspace, 2 workspaces, and 10 free model requests per day.Read 9 Oct 2026 · onuml.com

Plans and prices

Free Free forever 2 diagrams per project · 10 cloud projects per workspace · 2 workspaces · 10 free model requests per day · image upload not included Read 9 Oct 2026 · onuml.com
Starter $4.90, paid once one-time 240 credits · credits expire 6 months after issue Read 9 Oct 2026 · onuml.com
Pro $8 a month monthly; page also says “One-time payment” 500 monthly included credits · unlimited diagrams per project · unlimited cloud projects per workspace · unlimited workspaces · image upload included · no daily limit for free model requests Read 9 Oct 2026 · onuml.com
Popular $9.90, paid once one-time 500 credits · credits expire 6 months after issue Read 9 Oct 2026 · onuml.com
Pro Pack $19.90, paid once one-time 1,100 credits · credits expire 6 months after issue Read 9 Oct 2026 · onuml.com

Every OnUML plan and price →

Strong points and limits

Strong points

  • Generates diagrams from prompts and images
  • Visual and code editing with live preview
  • One-click Mermaid and PlantUML repair
  • PNG and SVG export
  • MCP supports several coding agents

Limits

  • Free plan limits diagrams and projects
  • Draw.io is not supported through MCP
  • Purchased credits expire after six months
  • Free plan excludes image upload

Who it suits

OnUML suits developers and diagram authors who want AI generation, code-based editing and browser access. It is also useful for teams connecting coding agents through MCP.

Verdict

OnUML combines AI diagram creation, UML editing, version history and MCP connectivity in a web app. Its free limits and expiring credit packs are explicit, while paid plans expand capacity.

Where Specifiction places it

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