Single tool with minimal definition quality. The tool 'get_carriers' has a reasonable name and basic schema, but critically lacks comprehensive description, parameter descriptions, output documentation, and error handling guidance. The description (71 chars) is below the rubric baseline (194 chars avg), and parameter descriptions are entirely absent. No output schema is documented. The implementation returns a hardcoded dict with no validation, error handling, or actual carrier lookup logic. This appears to be a skeleton/stub rather than a production-ready tool.

• Expand tool description to 150-250 characters. Example: 'Retrieve available shipping carriers for a given destination ZIP code and package weight. Returns carrier names, estimated delivery times, and base rates. Call this before offering shipping options to the customer. Returns empty list if no carriers service the ZIP.'
• Add descriptions to ALL input parameters. Example: dest_zip: 'The destination US ZIP code (5 digits, e.g. 90210). International postal codes not supported.'; weight_lbs: 'The total package weight in pounds (0.1 - 150 lbs). Packages over 150 lbs must use freight carriers.'
• Document the output schema explicitly. Example: 'Returns {"carriers": [{"name": string, "code": string, "delivery_days": number, "base_rate_usd": number}, ...]}. Always sorted by delivery_days ascending.'
• Add error handling with recovery guidance. Example: 'If no carriers found: 'No carriers available for ZIP {zip}. Check if ZIP is valid (5 digits). Consider splitting into multiple shipments or contacting customer service.'; 'If weight exceeds limits: 'Weight {weight} lbs exceeds carrier max (150 lbs). Suggest freight or split shipment to customer.'
• Implement actual carrier lookup logic instead of hardcoded return values. Validate ZIP code format (5 digits), weight range (>0, <=max), and return real carrier data.
• Add parameter constraints: dest_zip as a regex pattern '^[0-9]{5}$'; weight_lbs with minimum 0.1 and maximum 150.
• Consider pagination if carrier lists can exceed 20 items. Return {"carriers": [...], "total": number, "limit": 20} and accept a 'limit' parameter.