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

Annotations already cover the read-only, idempotent, non-destructive safety profile, so the description focuses on added context: prices are in USD, results carry a checkout_url that sends the buyer to shibaSIM, and how the data filter behaves for per-day versus fixed plans. That is genuine behavioral value beyond the structured fields.

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?

Four short sentences, front-loaded with purpose and followed by the facts an agent needs (currency, checkout_url, filter semantics). 'With factual filters' is the only slightly soft phrase, but there is no padding.

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 9-parameter search tool with no output schema, the description supplies the essentials: result currency, the presence of checkout_url in each result, and the data-filter interpretation. The gap is that two parameters (max_price_usd, min_validity_days) remain unexplained anywhere.

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 78%, so the baseline is 3; the description earns an extra point by clarifying that prices are USD (not stated for max_price_usd) and by restating that min_data_gb interprets as GB/day for per-day plans and total GB otherwise. It still says nothing about min_validity_days, which is undocumented in both places.

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 ('Search shibaSIM travel eSIM plans') plus a scoping constraint ('for one destination'). It does not explicitly name get_plan or list_destinations to differentiate itself, so it lands just 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?

The single-destination scope implies this is the browsing/filtering entry point versus a detail lookup, but the description never says when to prefer it over get_plan or when to call list_destinations first. Usage is inferable rather than stated.

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