Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds real value by disclosing the data basis ('based on the sight catalog only') and the exclusion boundary, though it says nothing about result limits or failure behavior for invalid city ids.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the action and scope, followed by the output inventory and the exclusion. Dense but every clause carries information given there is no output schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description compensates by enumerating exactly what the response contains (sight counts, days needed, strongest interests, indoor share, winner per interest, distances). An agent knows both how to call it and what it will get back.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3; the description earns above that by explaining that interests/periods are used to determine 'which city is stronger' and that trip_days drives how much of each city fits. It does not spell out the 2-4 city bound in prose, but the schema's minItems/maxItems already does.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (compare) and resource (two to four covered cities) with concrete examples of the question it answers. Clearly distinct from siblings like search_cities or get_city_guide because it is explicitly a side-by-side multi-city comparison.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Examples ('Porto or Lisbon?') plus the explicit exclusion list ('not prices, weather, nightlife or beaches') tell the agent when this is and isn't the right tool. It stops short of naming a specific sibling to use for the excluded topics, which is the only gap.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.