Generate PlantUML diagrams (sequence, class, activity) via plantuml-mcp-server (npx)

Recipe: Generate PlantUML diagrams via plantuml-mcp-server (npx)

Server: plantuml-mcp-server v0.2.4 by Infobip Transport: stdio via npx -y plantuml-mcp-server Auth: none — credential-free, zero config Renderer: uses plantuml.com online server (no local Java required)

Tools available (3)

MCP handshake

→ {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"agent","version":"1.0.0"}}}
← {"result":{"protocolVersion":"2024-11-05","capabilities":{"tools":{},"prompts":{}},"serverInfo":{"name":"plantuml-server","version":"0.2.4"}},"jsonrpc":"2.0","id":1}
→ {"jsonrpc":"2.0","method":"notifications/initialized"}

generateplantumldiagram — sequence diagram

→ {"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"generate_plantuml_diagram","arguments":{"plantuml_code":"@startuml\nactor User\nparticipant \"API Gateway\" as GW\nparticipant \"Auth Service\" as Auth\nparticipant Database as DB\n\nUser -> GW: POST /login\nGW -> Auth: validateCredentials()\nAuth -> DB: SELECT user\nDB --> Auth: user record\nAuth --> GW: JWT token\nGW --> User: 200 OK\n@enduml","format":"svg"}}}

← {"result":{"content":[{"type":"text","text":"{\n  \"success\": true,\n  \"url\": \"https://www.plantuml.com/plantuml/svg/NP1D2u9048Rl-ojUEjKXaeuUeioGFi10m_EaGosPnkvezE_RhGZg-ipxpZFCt0ePwQwreb9QWuDbesuEwLBVg14C5lir4XA-qsC0iaYAltadPsHiUbtoA-31JoGceIDPziCuKiexC9wvJI7sQPPZKhSdtQYayDJNG_HKwyfPbuOhRaHJROSZzNAvJ1o5o5QxrJ97vm-E8uo_LKzWk6nDzIbyN9iYXxGNVfiSz8U4c0O1qgsQSrEvFpm1\",\n  \"format\": \"svg\",\n  \"markdown_embed\": \"![PlantUML Diagram](...)\"\n}"}]},"jsonrpc":"2.0","id":3}

URL verification: curl -s -o /dev/null -w "%{http_code} %{content_type} %{size_download}B" → 200 image/svg+xml 8973B ✓

encode_plantuml — encode for URL embedding

→ {"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"encode_plantuml","arguments":{"plantuml_code":"@startuml\nBob -> Alice : hello\n@enduml"}}}

← {"result":{"content":[{"type":"text","text":"{\n  \"encoded\": \"SoWkIImgAStDuNBAJrBGjLDmpCbCJbMmKiX8pSd9vt98pKi1IW80\",\n  \"urls\": {\n    \"svg\": \"https://www.plantuml.com/plantuml/svg/SoWkIImgAStDuNBAJrBGjLDmpCbCJbMmKiX8pSd9vt98pKi1IW80\",\n    \"png\": \"https://www.plantuml.com/plantuml/png/SoWkIImgAStDuNBAJrBGjLDmpCbCJbMmKiX8pSd9vt98pKi1IW80\"\n  }\n}"}]},"jsonrpc":"2.0","id":3}

decode_plantuml — round-trip decode

→ {"jsonrpc":"2.0","id":4,"method":"tools/call","params":{"name":"decode_plantuml","arguments":{"encoded_string":"SoWkIImgAStDuNBAJrBGjLDmpCbCJbMmKiX8pSd9vt98pKi1IW80"}}}

← {"result":{"content":[{"type":"text","text":"{\n  \"decoded\": \"@startuml\\nBob -> Alice : hello\\n@enduml\"\n}"}]},"jsonrpc":"2.0","id":4}

Gotchas

• stdin must stay open: the server exits immediately when stdin closes. Keep the pipe alive for at least 10s after sending the tools/call (the online renderer takes a few seconds).
• format options: only svg and png are valid.
• output_path: optional local file save, restricted to CWD by default. Set PLANTUML_ALLOWED_DIRS env var for other directories.
• Syntax validation: generate_plantuml_diagram auto-validates PlantUML syntax and returns structured errors for invalid code, enabling auto-fix loops.