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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so the safety profile is covered. The description usefully adds that results are sorted by eSIM-Global.VIP Data Rating and that prices and a direct link are included, but it says nothing about rate limits, caching, or whether the destination lookup is exhaustive.

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, front-loaded with what the tool does, then what it returns, then when to use it. No filler, and every sentence carries information an agent needs.

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 annotations covering safety, a fully documented schema, and an output schema handling return values, the description is close to complete. The minor gap is that it does not route the agent among the three sibling tools, and it partially duplicates output-schema territory by describing the result contents.

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 all four parameters (including the city-to-country mapping rule for destination and the currency/language derivation) are already documented in the schema. The description only restates the destination as "country or region" and adds no new meaning, so the baseline 3 applies.

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 (Find) and resource (eSIM plans) scoped to a destination, and adds the return shape (best-value plans with prices and a link). It does not explicitly distinguish itself from the siblings get_plan_details or start_checkout, so an agent must infer the boundary between searching, inspecting, and purchasing.

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?

"Use when a user wants mobile data abroad" gives a clear triggering context for the agent. However, it names no alternatives and states no exclusions, so the agent gets no help deciding when to jump to get_plan_details or start_checkout instead.

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