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

Annotations already declare readOnlyHint=true and openWorldHint=true, and the description adds useful behavioral context beyond that: non-refundable once bought, each plan includes an order_url, and pricing currency depends on country/request origin. It does not cover rate limits or full result contents, but it adds material purchase-relevant context.

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 compact and front-loaded, first stating what the tool returns and then covering optional filters, purchase implications, and currency semantics. Every sentence contributes useful information.

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 two-parameter search tool with no output schema, the description is largely complete: it explains the product type, optional country and currency filters, order_url presence, refund policy, and pricing currency behavior. The main missing piece is explicit differentiation from the sibling search_esim_plans tool.

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 are already well documented. The description repeats the country options and currency behavior rather than adding new syntax, constraints, or examples beyond the schema.

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 states a specific resource and scope: eSIM plans with a real carrier phone number, including calls, texts, data, and prices. It clearly distinguishes phone-number eSIMs from generic eSIMs conceptually, but does not explicitly name or contrast with the sibling search_esim_plans tool.

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 implies when this tool is useful by specifying phone-number eSIMs and optional country/currency filters, but it gives no explicit when-to-use versus search_esim_plans guidance or exclusions. 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.