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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds non-obvious value by enumerating the topical coverage of the returned facts and flagging that content is unstructured prose ('in the shop's own words'), which helps the agent anticipate the response shape. It does not discuss output format or freshness, but the output schema exists.

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, no filler: the first defines the content, the second defines the routing rule. The usage rule is front-loaded second, right where an agent deciding between siblings will look.

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 zero parameters, an output schema present, and annotations covering the safety profile, the only remaining burden is scope and routing — both delivered precisely. Nothing needed to call this correctly 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?

The tool takes zero parameters, so the baseline is 4. There is nothing for the description to disambiguate; its content list is a faithful preview of the result rather than parameter guidance.

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 the resource (shop-level facts about how eSIM-Global.VIP works) and enumerates the exact content domains it covers: delivery/installation, device requirements, payment, guarantee, top-up, hotspot, support, company details. The closing clause explicitly demarcates it from plan-specific siblings, so an agent can route without opening a schema.

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 a clear usage trigger ('any how / when / what if question') plus an explicit exclusion ('not about one specific plan'). It stops short of naming get_plan_details or search_esim_plans as the alternative for the excluded case, leaving that inference to the agent.

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