Diagrams.so vs OnUML
Diagrams.so
diagrams.soOnUML
onuml.comSide by side
| Figure | Diagrams.so | OnUML |
|---|---|---|
| Price from | $10/mo | $8/mo |
| Free plan | Yes | Yes |
| Free trial | — | — |
| Open source | — | — |
| Web | Yes | Yes |
| API | Yes | Yes |
| Plans published | 3 | 5 |
| Spec score · AI Diagram Generators | 8.2 (#11) | 7.7 (#20) |
| Integrations | The product offers a REST API, MCP server, and Python and TypeScript SDKs, and names Claude, Cursor and VS Code as MCP clients. | Its remote MCP server connects to coding agents including Codex, Claude Code, Cursor, and OpenClaw. |
| Support | The Power plan includes priority support, and the About page lists [email protected] for questions, feedback and partnership inquiries. | The site lists [email protected] as its contact email. |
| Usage limits | The FAQ says prompts are limited to 30,000 characters, custom icon sets are not supported in the generator, and very large diagrams may take longer to generate or open. | The free plan allows 2 diagrams per project, 10 cloud projects per workspace, 2 workspaces, and 10 free model requests per day. |
Plans
OnUML
- FreeFree
- Starter$4.90, paid once
- Pro$8 a month
- Popular$9.90, paid once
- Pro Pack$19.90, paid once
In their own words
Diagrams.so
Diagrams.so turns written descriptions into editable architecture diagrams, saved in Draw.io format. It generates flowcharts, sequence diagrams, entity relationship diagrams and cloud infrastructure diagrams, with official AWS, Azure, Google Cloud Platform and Kubernetes icon libraries alongside network, database, security and general-purpose shapes. Opinionated Mode can suggest missing components; non-blocking warnings flag risks such as single-AZ deployments and publicly exposed resources. Diagrams export as.drawio XML, PNG or SVG, and.drawio files open in Draw.io, Confluence, VS Code and Notion. Users can import.drawio files on every plan and compare or restore versions using history. The product offers a REST API, MCP server, and Python and TypeScript SDKs, with Claude, Cursor and VS Code listed as MCP clients. Free includes five credits, requires a BYO LLM key and watermarks exports. Free-tier diagrams are public; private diagrams require Pro or Power. Pro costs $10 a year billed annually or $15/mo billed monthly; Power costs $16.67 a year billed annually or $25/mo billed monthly.
OnUML
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.