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

The annotations already declare readOnlyHint=true, so the description only needs to add behavioral details. It does so by explaining that the output format changes when the country parameter is passed (listing individual airports with minimum stops) and that results are aggregated by stop count and country. This goes beyond the annotations and gives the agent useful calling context.

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?

The description is two sentences, front-loaded with the core purpose and output shape, and then clarifies the country parameter's effect. Every sentence earns its place with no redundant or vague wording.

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?

For a read-only tool with good annotations and a fully described schema, the description is sufficiently complete. It explains both default behavior (totals and breakdowns) and the optional country-driven detail output, so an agent understands what to expect without an output schema. No obvious call context 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%, so baseline is 3. The description adds meaning by tying max_stops to 'stop budget' and explicitly explaining that the country parameter switches the output from totals/breakdowns to a per-airport list with minimum stops. This reinforces the schema and clarifies how the parameters affect results.

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?

The description clearly explains what the tool computes: network reachability from one airport within a stop budget, returning totals, stop-count breakdowns, and country breakdowns. It also specifies that providing a country lists individual reachable airports with minimum stops. This distinguishes it from siblings like destinations_from by focusing on stop-budget reachability rather than simple destination listings.

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?

The description implies usage context (when you need reachability within stop constraints and aggregate/country breakdowns) but does not explicitly mention alternatives or when not to use this tool. There is no reference to sibling tools or any exclusions, so guidance is only implied.

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