The Penrose MCP server provides 4 tools with explicit schemas and basic descriptions, but has significant gaps in parameter documentation, output schema clarity, and error handling guidance. Tool names follow verb_noun conventions (create_*, generate_*), which is good. However, most parameters lack individual descriptions, they are defined in the schema with minimal context. Output schemas are not documented in the tool descriptions, forcing LLMs to infer what fields they'll receive. Error handling is absent: there are no recovery hints, no invalid-input guidance, and no classification of error types. The server implements resources correctly and has in-memory storage, but the tool interface itself is underspecified for production use.

• Add 50-100 character descriptions to every parameter in every tool schema. For example, in create_domain, describe 'predicates' as 'Array of logical predicates that apply to this type, each with a name and argument types. Example: {name: "Parallel", args: ["Line", "Line"]}'. For 'constraints' in create_style, clarify whether they are CSS constraints, mathematical expressions, or Penrose-specific syntax.
• Document output schema for each tool in its description and in the response. Example for create_domain: 'Returns {name: string, types: [...], id: string, created_at: ISO8601}'. Example for generate_diagram: 'Returns {diagram_format: "SVG", data: string, width: number, height: number, status: "success"}'. This enables LLMs to plan downstream calls.
• Add error handling guidance to each tool description. Example: 'If the referenced domain does not exist, returns error code DOMAIN_NOT_FOUND with message "Domain {domain_name} not found. Use create_domain to create it first." This is retryable after domain creation.'
• Constrain the 'variation' parameter in generate_diagram with an enum or description. Example: 'variation (optional, string): Controls diagram layout and style. Valid values: "default", "compact", "detailed". Defaults to "default".'
• Add length and format constraints to all name/ID parameters. Example: 'name (string): Domain name. Must be 1-50 characters, alphanumeric plus underscore.'
• Document idempotency in tool descriptions. Example: 'Idempotent, calling create_domain twice with the same parameters returns the same domain object (no duplicate created). If a domain with this name already exists and types differ, returns error CONFLICT.'