ON-UML / MODEL CONTEXT PROTOCOL

Connect your coding agent to the OnUML MCP server.

The OnUML MCP server connects coding agents like Codex, Claude Code, Cursor, and OpenClaw to your diagram workspace. Discover the workspaces you can access, read diagram source, and make deliberate updates without leaving the conversation.

Create an API key View setup

WHAT YOU GET

What can the OnUML MCP server do?

Find the right context

Start with the workspace visible to the signed-in account, then narrow to folders and projects.

list_workspaces
list_folders
list_projects

Read the diagram before changing it

Read the project structure and current diagram source before making a change.

get_project
get_diagram

Create and update safely

Create projects and diagrams without duplicating retries or overwriting newer edits.

create_project
create_diagram
update_diagram

THE SHORT ANSWER

What is the OnUML MCP server?

It is a remote MCP server that lets an AI coding client work with the diagrams and projects available to your OnUML account. Access always follows your current workspace permissions.

Use it when a diagram belongs in the same workflow as the code: explore a project, inspect the current source, update a Mermaid or PlantUML diagram, or create an OnUML mind map. You can still review the result in the OnUML diagram editor.

CONNECT IN MINUTES

Connect OnUML MCP to your coding agent.

STEP 01
Create a key
Open OnUML API key settings while signed in. Copy the secret immediately; OnUML never shows it again.
STEP 02
Paste your token
Replace YOUR_ONUML_TOKEN_HERE in the command or personal configuration file. Keep that file out of Git.
STEP 03
Add the remote server
Use the configuration for your client. The MCP endpoint is https://onuml.com/mcp.

ONE-COMMAND SETUP

codex mcp add onuml --url https://onuml.com/mcp && printf '\n[mcp_servers.onuml.http_headers]\nAuthorization = "Bearer YOUR_ONUML_TOKEN_HERE"\n' >> "$HOME/.codex/config.toml"

Replace YOUR_ONUML_TOKEN_HERE with your API key before running.

Codex

config.tomlREMOTE MCP

[mcp_servers.onuml]
url = "https://onuml.com/mcp"
http_headers = { Authorization = "Bearer YOUR_ONUML_TOKEN_HERE" }

Add the token directly to your personal Codex configuration. The desktop app, CLI, and IDE extension share this file on the same host.

CONFIG LOCATION

~/.codex/config.toml

Codex · Read MCP docs

WRITE WITH CONTEXT

Changes are designed to be recoverable.

The agent reads the latest diagram before making a change. If someone else has edited it first, OnUML stops the update instead of overwriting their work.

Access follows your current permissions

The agent only sees workspaces and projects your OnUML account can currently access.

Retries do not create duplicates

If a network request is retried, OnUML prevents the same project or diagram from being created twice.

Updates protect newer work

If someone changes the diagram first, the agent must reload it instead of overwriting the newer version.

GOOD TO KNOW

OnUML MCP server FAQ.

Which diagram types can an agent work with?

Agents can read and update Mermaid, PlantUML, and OnUML mind maps. Draw.io diagrams are not currently supported through MCP.

What happens when a key is revoked or expires?

The client immediately loses access. Create a replacement key in API key settings and replace the token in your client configuration.

Which workspaces can an agent access?

Only the workspaces and projects your OnUML account can currently access. If your permissions change, MCP access changes with them.

Ready to give your agent diagram context?

Create a key, connect one client, then start with list_workspaces.

Open API keys