The ExpenseTracker server provides three well-named tools with explicit input schemas and descriptions. However, there are meaningful gaps in schema completeness, output documentation, error handling guidance, and parameter constraints that prevent a higher score. All tools are properly registered via @mcp.tool() decorators in main.py with async implementations. Tool names follow verb_noun convention (add_expense, list_expenses, summarize). Descriptions are present and adequate (45 - 90 chars) but lack critical details about return formats and error scenarios. Input schemas declare types (string, number) and descriptions for all parameters, but are missing important constraints: date parameters lack format specs, numeric amount lacks min/max bounds, category lacks enum or validation guidance. Output schemas are entirely undocumented, callers cannot plan downstream operations without seeing the actual responses. Error handling exists but returns generic 'status: error' responses without actionable recovery guidance. Parameters have sensible defaults (subcategory='', note='', category=None) and are not overly required.

• Document output schema for each tool. Example for add_expense: 'Returns {status: "success"|"error", id: <integer>, message: <string>}.'
• Add date format constraints to all date parameters. Change description to: 'Date in YYYY-MM-DD format (e.g. 2024-01-15). Must be between 1900-01-01 and 2099-12-31.'
• Add min/max bounds to amount parameter: 'Amount in decimal format, must be > 0 and <= 999999.99 (e.g. 15.50).'
• Declare valid categories as an enum in the schema, or add description: 'Category must be one of: [retrieve from expense:///categories resource]. Invalid category will be rejected.'
• Add pagination support to list_expenses: include optional limit (default 50, max 100) and next_cursor parameters. Document in description: 'Returns up to {limit} results. Use next_cursor in subsequent calls to fetch more.'
• Make error responses actionable. Change catch blocks to return: 'Invalid date format: expected YYYY-MM-DD. Example: 2024-01-15.' or 'Failed to add expense. Verify all required fields are present and try again.'
• Add validation to list_expenses: 'start_date must be <= end_date. Typical range is 30 - 365 days for performance.'
• Include per-item success/failure in responses if tool supports batch operations (future enhancement).
• Validate category input in add_expense before INSERT. Return clear error if not in allowed set.