Mermaid-MCP has significant definition quality gaps. While both tools are explicitly registered with names and basic descriptions, the schema definitions are incomplete, parameter descriptions lack constraint information, and output schemas are entirely undocumented. The generate_chart tool accepts 6 parameters but provides minimal guidance on valid values, formats, or dependencies. The descriptions are present but generic (10-50 chars for params). No error handling guidance is provided to help LLMs recover from failures. The server returns PNG binary data without documenting the response structure, field names, or how downstream tools should handle the output.

• Add explicit enum constraints for 'chart_type' parameter: 'chart_type (string, enum): The diagram type. Valid values: flowchart, sequence, gantt, class, state, pie, bar. Default: flowchart.'
• Add min/max bounds to numeric parameters: 'width (integer, range 200 - 4000, default 800): Image width in pixels.' Similarly for height.
• Document output schema as a structured response object in tool definition. Both tools should return: {success: boolean, data?: {mimeType: string, filename: string, base64Content: string}, error?: {code: string, message: string, suggestion: string}}
• Replace PNG error responses with structured JSON error objects that include actionable guidance. Example: {error: {code: 'invalid_chart_type', message: 'Unknown chart type: "swimlane". Valid types are: flowchart, sequence, gantt, class, state, pie, bar.', suggestion: 'Did you mean "sequence"?'}}
• Clarify input_text format: 'input_text (string, required): Raw Mermaid diagram code (e.g., "flowchart LR\n A --> B") or natural language description (e.g., "Create a flowchart from step A to step B"). If natural language, the server will convert to Mermaid syntax via LLM.'
• Document css_template and custom_css interaction: 'css_template and custom_css are mutually exclusive. If both provided, custom_css takes precedence. Use css_template for built-in themes or custom_css for inline style overrides.'
• Change list_css_templates to return structured JSON (array of template objects with name, description, preview_url) instead of PNG. Or rename to 'generate_css_templates_preview' to match actual behavior.

Inferred effective spec: <=2025-11-25.

• Relies on Logging (deprecated) - log to stderr or use OpenTelemetry