plantuml-mcp

Render PlantUML diagram

render_diagram

Render PlantUML code into PNG, SVG, or ASCII art; returns PNG inline for inspection, SVG/TXT as text, optionally saves to a file, and reports syntax errors with the offending line.

Instructions

Renders PlantUML code (class, sequence, use case, activity, component, state, deployment, ER, mindmap, gantt...) into an image. PNG is returned inline so it can be inspected; SVG/TXT are returned as text. Optionally saves the result to output_path. Reports syntax errors with the offending line.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "code": "<code>"
    },
    "name": "render_diagram"
  }
}

Input Schema

Name	Required	Description	Default
`code`	Yes	PlantUML source. @startuml/@enduml is added automatically if missing.
`format`	No	Output format (txt = ASCII art)	png
`output_path`	No	File path to save the rendered diagram to

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Oct 21, 2026

TDQS

A4/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full behavioral burden and discloses key traits: PNG is returned inline, SVG/TXT are returned as text, output can be saved to a path, and syntax errors are reported with the offending line. It does not mention rate limits, permissions, or whether saving overwrites an existing file, but covers the primary behaviors well.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the core action, then efficiently layers in output behavior, saving, and error reporting. Every sentence adds useful information without redundancy.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given no annotations and no output schema, the description must explain return behavior and error handling. It does so clearly: inline image vs text output, optional file save, and syntax error reporting. An agent has what it needs to invoke the tool correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the baseline is 3. The description adds meaning beyond the schema by clarifying that PNG is returned inline for inspection while SVG/TXT are returned as text, and that output_path is an optional save location. It adds behavioral context to the format enum rather than just restating it.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb ('Renders') and resource ('PlantUML code') and enumerates supported diagram types and output modes. However, it does not explicitly distinguish itself from the sibling tools (get_diagram_urls, decode_diagram_url), so the differentiation remains implicit.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage ('Renders PlantUML code') and gives a condition for optional saving ('Optionally saves the result to output_path'), but provides no explicit when-to-use guidance or alternatives to the sibling tools. Usage is inferable but not directed.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Deploy Server