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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavior beyond that: a deterministic ordering (cheapest first, then single-country before multi-country), which materially affects how an agent reads the returned list.

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?

Two short sentences, no filler. The most decision-relevant fact (what it lists and the ordering) is front-loaded, and the filter summary follows.

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 read-only search tool with full schema descriptions and no output schema, the description covers selection and ordering, which is most of what an agent needs. It is only slightly thin on the shape of a returned 'plan' and how limit interacts with the result set, but those are minor given the rich parameter descriptions.

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 every parameter (lang, limit, min_gb, min_days, plan_type, destination) is already documented in the schema, including enum meanings and defaults. The description only names three filters already fully covered there, adding no syntax, units, or edge-case detail beyond the schema; baseline 3 applies.

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 verb and resource ('List plans for a destination') and even specifies the result ordering (cheapest first, single-country before multi-country). It is clear what the tool returns, but it never differentiates itself from siblings like recommend_plan or get_plan, which an agent could plausibly confuse with a plan-listing/search 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 only guidance is 'Filter by trip length, minimum GB, and plan type,' which restates filter parameters rather than saying when to choose this tool over recommend_plan or estimate_data. There is no when-not guidance and no mention of prerequisites or follow-up tools (get_plan, get_purchase_link).

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