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

Annotations already cover readOnly/idempotent/openWorld=false. The description adds real context beyond them: results are filtered to plans on sale now, sorted cheapest-first, priced in USD charged at checkout, and each carries a buy_url for that exact plan.

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?

Front-loaded with the core action and the primary parameter, then layered with parameter guidance and return behavior. Dense but each sentence carries information; slightly long, keeping it from a 5.

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 an 8-parameter, no-output-schema tool, it covers parameter routing, filtering, sort order, currency, and return fields (buy_url, coverage). An agent has everything needed to call it correctly.

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 100%, so baseline is 3; the description nonetheless adds meaning by explaining that country_code accepts ISO or catalogue codes and returns single-country plus regional/global plans (with a coverage field), and that region targets multi-country plans.

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 (search) and resource (SimAbroad eSIM plans) with a clear scope (for a trip). It is easily distinguished from siblings: it references list_destinations as the source of codes and get_buy_link implicitly via the buy_url/checkout behavior.

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?

Gives clear routing between country_code and region ('Or pass region for multi-country plans') and explains how to use min_validity_days/min_data_gb/unlimited. It lacks explicit when-not-to-use guidance or a named alternative for other flows, so it stops short of a 5.

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