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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, non-destructive, openWorldHint false). The description adds useful detail about returned content (data, validity, network, 5G, top-up, carriers, price, checkout link), but it discloses nothing about authentication, rate limits, errors, or other behavioral traits beyond the annotations.

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?

The description is a single front-loaded sentence that lists the returned fields with no filler. Every item is relevant to a get-one-plan operation.

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 read-only tool with rich annotations and no output schema, the description usefully enumerates returned fields. However, it leaves plan_id unexplained and does not describe response structure; the schema covers the other parameters, so the remaining gaps are moderate.

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 schema describes days and lang thoroughly, including lang's purchase-page effect and default. plan_id is undocumented in both schema and description. The description mentions only 'one plan' and adds no parameter syntax, constraints, or meaning, so it does not compensate for the 67% schema description 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?

The description identifies a specific verb (details) and resource (one plan) and enumerates returned fields such as data, validity, network, and price. It is clear for a fetch-by-id tool, but it does not distinguish this from siblings like get_purchase_link, which likely also returns a checkout link, or search_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?

The description provides no when-to-use guidance, no conditions for choosing this tool over alternatives such as search_plans or recommend_plan, and no prerequisites or exclusions. It only describes what the tool returns.

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