Single tool with adequate naming (render_diagram) but significant gaps in schema documentation and parameter descriptions. The tool description is moderately detailed (195 chars) but the input parameter lacks a proper schema with type constraints. No output schema is documented. The implementation includes validation logic but error handling is not surfaced to the LLM. No tool annotations (readOnlyHint, etc.) present.

• Define input schema with nested object structure: spec.nodes (array of objects with id, type, label, x, y, w, h), spec.edges (array with from, to), spec.direction (enum: LR|RL|TB|BT), spec.router (enum: straight|curved), spec.col_gap/row_gap/margin (numbers), spec.defs (string). Mark nodes and edges as required.
• Document output schema: 'Returns an SVG string (1KB - 10MB) containing a rendered diagram. On validation error, raises ValueError with a list of constraint violations (e.g., "nodes[0]: missing id", "edges[1]: from references unknown node").'
• Expand parameter description to list required fields, valid node types (box, circle, text, database, stack, group, note, custom), and valid edge properties. Include a minimal example: '{"nodes": [{"id": "a", "type": "box", "label": "start"}], "edges": [{"from": "a", "to": "b"}]}'.
• Add error recovery guidance: 'If validation fails, the error message lists missing or invalid fields. Ensure all nodes have unique ids and types, all edges reference existing node ids, and numeric gaps are non-negative.'
• Add tool annotation in FastMCP: @mcp.tool(readOnlyHint=True) to signal that render_diagram does not modify state and is safe to call multiple times.