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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds only that the response is the 'full detail' and mentions two fields (price_token, unlimited), which is thin given an 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?

A single front-loaded sentence with no filler. The trailing mention of price_token and unlimited is slightly wasteful since an output schema already describes the return shape.

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 simple, non-destructive lookup with annotations and an output schema, the description covers the essentials. The unlabeled localization parameter (lang) and any error behavior for an unknown catalog_id are left unexplained.

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 coverage is 50%: catalog_id is already documented in the schema as coming from get_esim_plans, and the description simply restates that keying. The lang parameter (enum en/es) is undocumented in both places, so the description does not compensate for the coverage gap.

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 action (fetch full detail) on a specific resource (one eSIM plan) keyed by catalog_id, which implicitly contrasts with the bulk get_esim_plans sibling. It stops short of naming the sibling explicitly, so an agent must infer the single-vs-list distinction from the wording.

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 'by catalog_id' phrasing implies this is called after listing plans to drill into one entry, but no when-to-use or when-not-to-use guidance is stated and no alternative is named. Usage is inferable rather than instructed.

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