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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds only that the response includes data, validity, network, top-up support, transparency, reviews and a link, which is largely restated by the output schema rather than adding behavioral context such as rate limits or freshness.

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?

A single front-loaded sentence that leads with the action and resource, then lists the payload. Every clause carries information and there is no filler.

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 a full output schema and annotations covering safety, the description only needs to identify the resource and lookup key, which it does. It is essentially complete, though a brief pointer to the search-to-details workflow would close the remaining gap.

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 both parameters (including language and its effect on the link's language/currency) are already fully documented. The description mentions only 'by product id' and adds no syntax, format, or constraint detail beyond the schema, which is the baseline 3 case.

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 ('Full details for one eSIM-Global.VIP plan') and the key it is addressed by ('by product id'), plus an enumeration of the fields returned. This implicitly separates it from the list-oriented search_esim_plans, but it never names that sibling, so it falls short of a 5.

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?

Usage is only implied: 'Full details ... by product id' suggests it is the follow-up call once an id is known, contrasting with the summary results of search_esim_plans. There is no explicit when-to-use statement and no stated conditions or exclusions, so it is minimal viable guidance.

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