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

Annotations already declare readOnly/openWorld=false and non-destructive, so the safety profile is covered. The description adds non-obvious behavior beyond that: the strict matching rule that silently excludes regional plans, and the default-inclusive filter semantics — both are things an agent would otherwise get wrong.

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 front-loaded sentences with the matching pitfall placed early, where it matters most. The sentence enumerating catalog_id, price_token, and unlimited is partially redundant given an output schema exists, but it is short enough not to be a real cost.

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?

Annotations and an output schema carry much of the burden, and the description covers the highest-risk parameter well. However, for a 5-parameter filtering tool with three enum parameters, leaving coverage_type undocumented and lang/currency undefined is a noticeable gap an agent cannot resolve from the schema alone.

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 40%, so the description must compensate and only partly does. It thoroughly explains country_iso's strict-match behavior and the data_type default ('omit or all returns both'), but lang, currency, and coverage_type receive no mention anywhere — coverage_type in particular is a bare string with no enum and no explanation.

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?

Opens with a specific verb and resource ('List publishable travel eSIM plans for a destination') and scopes the result set with 'publishable'. It implicitly separates itself from get_esim_plan_detail and get_esim_topup_plans via the list-vs-detail distinction, but never names a sibling explicitly.

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 actionable routing logic: use ISO-2 for a single country, region slugs (eu, ww, as) for regional or global coverage, and clarify that 'es' will not return EU/global plans. That is a real usage rule most tools lack, though no alternative tool is named for the detail-heavy case.

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