OnUML vs OpenCharts

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.

OpenCharts is an AI workspace for flowcharts, presentations, notes, code, video, and agents. Theo AI can create these materials from plain-language descriptions. Flowcharts use terminal, process, decision, and data nodes on an infinite canvas, with automatic layout and export tools. The presentation editor supports editable slides, speaker notes, transitions, AI generation, rehearsal coaching, web publishing, and PPTX export. Theo Agents can start on schedules, webhooks, monitoring triggers, or manually; they can use external connectors, human approval gates, and produce deliverables. Connectors include Stripe, HubSpot, Slack, Google Sheets, Discord, Notion, GitHub, and others. A REST API manages project types, and the Theo MCP server provides 113 tools and five readable resources. Each account starts with 10 GB of Drive storage, including Free Forever. That plan costs nothing and includes 500K AI credits and one of each project type. Starter costs $9.99 a month, Pro $24.99 a month, and Teams $14.99 a month with a three-user minimum. OpenCharts says it does not use customer data to train or fine-tune AI models.