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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds capability-boundary context the annotations cannot: that no continent/region/theme grouping exists and that only destinations (not tours) are returned. It stops short of any note on pagination or result limits.

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?

Three short sentences, zero filler, with the core capability and the default scope front-loaded ahead of the exclusion clause.

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 an output schema present, return shape need not be described, and the description covers scope semantics, defaults, and the key negative constraint. Nothing an agent needs before calling this read-only listing tool is missing.

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 description coverage is 100% and all four parameters are documented there, so the baseline is 3. The description only restates the scope enum and adds that 'cities' pertains to one country, which is useful but marginal over the schema.

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 and resource ('Lists catalogue countries and cities') plus the payload ('their published tour counts'). The closing line 'Returns destinations only, not tours' explicitly separates it from the tour-oriented siblings (search_tours, get_tour, compare_tours).

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?

Gives the three valid scopes with the condition that selects each ('cities (of one country)', 'featured (default)'), and rules out unsupported groupings. It never names a sibling tool to use instead for tour data, so the routing guidance is implicit rather than explicit.

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