ArchitectureDiagram.ai vs OnUML

ArchitectureDiagram.ai turns natural-language descriptions into architecture diagrams that users can refine through chat-based editing. It supports Mermaid flowcharts, draw.io diagrams, Excalidraw sketches, and AI-generated images, with 24 templates for patterns such as microservices, serverless, Kubernetes, and RAG pipelines. Party Mode generates image candidates from multiple models in parallel for comparison. Diagrams can be downloaded as PNG, copied to the clipboard, shared through public read-only links, or embedded in supported wikis. Present view creates.pptx and.pdf decks with speaker notes on Hacker and higher plans. Expert Chat for architecture feedback is included on Hacker and higher; Free and Builder users get three review messages total across diagrams. The web product has a free plan with two diagrams per month and paid plans starting at $4.99 per month. The API uses bearer keys to generate Mermaid text synchronously or rendered PNG images asynchronously; listed generation costs are $0.05 and $0.20 respectively. Generation history is saved for up to 50 items. The privacy policy says prompts and generated outputs are retained to improve generation.

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.