The pycentauri MCP server demonstrates solid definition quality with clear tool names, consistent verb-prefix patterns, and detailed descriptions. All 13 tools are explicitly registered in src/pycentauri/mcp/server.py with FastMCP decorators. Tool names follow verb_noun convention (get_status, start_print, set_temperatures). Descriptions are comprehensive (194 chars avg, well within 10-1024 range), explain WHEN to use each tool, and correctly mark destructive/reversible operations. Input schemas are present and typed for all tools. However, there are notable gaps: (1) several tools lack parameter descriptions despite having schema definitions (e.g., set_print_speed mode parameter has description, but upload_file and several control tools lack full descriptions for all params), (2) some output schemas are partially documented in-code comments but not formally exposed as returnType metadata, (3) error handling guidance is minimal, most tools lack recovery suggestions, and (4) parameter constraints are described textually but not always enforced as enums or format validators. The server demonstrates good composition (tools are focused, single-responsibility), proper naming (distinct from each other), and appropriate security (host injected via environment, not tool params). This places it solidly in the B+ range (70-79).

• Add enum constraint to set_print_speed mode parameter: {type: 'string', enum: ['silent', 'balanced', 'sport', 'ludicrous']} OR {type: 'integer', enum: [50, 100, 130, 160]}. This prevents hallucinated values.
• For every tool, add error recovery guidance. E.g., 'If connection fails, verify PYCENTAURI_HOST is set and the printer is on the network. Retry after 5 seconds.' This guides LLM retry logic.
• Formalize output schemas using TypedDict or JSONSchema returnType. Define structure of get_status return (fields: host, state, print_status, progress, filename, layer, temperatures, position, z_offset, fans, raw) so clients can plan downstream operations.
• Add a confirm_print tool or mode flag to start_print. Instead of relying on agent to ask user, tool returns a result: {action: 'input_required', error: 'User confirmation required before starting print. Confirm with confirm_print(filename, storage).'}. This implements the MRTR (Multi-Round-Trip Request) pattern.
• Add schema-level validation: set_fan_speed and set_temperatures should use minProperties: 1 to enforce at least one parameter. Alternatively, return clear error: 'At least one of model, auxiliary, or chamber must be specified.'
• Document discover_printers return structure in a formal way. Either add a typed return annotation or schema definition, or include a note: 'Each printer dict contains: host (string), mainboard_id (string), name (string), machine_name (string), firmware_version (string).'
• Expand upload_file and start_print descriptions to clarify dependencies: 'Call upload_file first with a local .gcode or .ufp file. Then call start_print with the returned filename.' This hints at tool chaining.