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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world, so the safety profile is covered. The description adds non-annotation context: results are 'live' (current pricing), priced in USD, and normalize to a price-per-GB figure. It stops short of describing 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?

Two tight sentences with no filler: the first front-loads what is returned, the second covers the required destination format and optional filters. Every clause earns its place.

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 carries the return-shape burden and does so by naming the four returned attributes. Combined with the 100%-covered input schema and explicit code-source guidance, an agent has everything needed to call this correctly.

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 the schema already documents all three parameters, giving a baseline of 3. The description adds mild value by clarifying that destination accepts an ISO-2 code or a code from list_esim_destinations and that min_gb/min_days narrow the list, but this largely restates 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 (live travel eSIM plans for one destination) and enumerates the returned fields: data GB, validity days, price USD, price per GB. It distinguishes itself from list_esim_destinations by referencing it as a code source, but does not explicitly differentiate from the sibling get_topup_plans.

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 concrete usage guidance: supply an ISO-2 country code (with examples TR, JP, US, GB) or a destination code obtained from list_esim_destinations, and notes the filters are optional narrowing. No explicit when-not-to-use or alternative-selection rule, but the context is clear.

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