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Diagrams MCP

by io.github.mskry

render_plantuml

Read-only

Render a PlantUML diagram definition and return the image.

The definition should be valid PlantUML syntax wrapped in @startuml/@enduml (sequence, class, component, activity, state, deployment, etc.).

Args: definition: PlantUML diagram definition text. filename: Output filename without extension. format: Output format — "png" (default) or "svg". PDF is not supported (requires Batik/FOP). download_link: If True, return a temporary download URL path (/images/{token}) that expires after 15 minutes; if False, return inline image bytes. Defaults to True (URL) — set DIAGRAMS_INLINE_DEFAULT=true on the server to flip the default. SVG and PNGs larger than the inline limit always use a download link.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
formatNopng
filenameNodiagram
definitionYes
download_linkNo

TDQS

A4.4/5.0
Behavior4/5

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

Beyond the readOnlyHint annotation, the description discloses download link expiration (15 minutes), inline vs. download behavior, default download_link value, and server-side environment variable influence. This gives significant behavioral context, though it does not cover error handling.

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 purpose, uses a clean Args structure, and every sentence conveys necessary details without fluff. It is appropriately sized for the tool's complexity.

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?

With no output schema, the description fully covers return formats (image bytes or download URL), defaults, and exceptions (inline limit). It provides enough information for an agent to invoke the tool correctly without ambiguity.

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

Parameters5/5

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

Despite 0% schema description coverage, the Args section explains each parameter in detail, including format enum semantics (PDF unsupported) and download_link behavior (URL vs bytes, defaults, and server configuration).

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

Purpose5/5

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

The description opens with a clear verb+resource: 'Render a PlantUML diagram definition and return the image.' It also enumerates supported diagram types (sequence, class, component, activity, state, deployment), making it distinct from sibling render_mermaid.

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 for PlantUML syntax (wrapped in @startuml/@enduml) but does not explicitly compare against sibling render_mermaid or render_diagram. It notes that PDF is unsupported, providing a limitation, but no alternative tool is suggested.

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

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TDQS

A4.6/5.0
Disambiguation5/5

Each tool serves a distinct purpose: browsing (list_providers, list_services, list_nodes, search_nodes), equivalence lookup (find_equivalent, list_categories), and rendering in three different syntaxes (render_diagram, render_mermaid, render_plantuml). No two tools overlap in function, and descriptions clearly differentiate when to use each.

Naming Consistency5/5

All tool names follow a consistent verb_noun pattern with lowercase snake_case: list_* for browsing, render_* for output generation, find_equivalent, and search_nodes. The pattern is predictable and aids agent understanding.

Tool Count5/5

With 9 tools, the server is well-scoped: 4 browsing tools, 2 equivalence tools, and 3 rendering tools cover the diagram creation workflow without bloat. Each tool earns its place.

Completeness5/5

The tool surface supports the full workflow: discover providers/services/nodes, search for equivalent roles, and render diagrams in Python, Mermaid, or PlantUML. No obvious gaps exist for the stated purpose.

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