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

Annotations already cover safety (readOnlyHint, destructiveHint=false), so the description earns credit for adding domain behavior beyond them: a plan failing the filters is 'not found', the response includes purchase_url, and figures are labelled indicative — a real caveat about data trustworthiness. It stops short of describing error shapes or latency/freshness of pricing.

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?

Three short sentences, front-loaded with the return value, then the failure condition, then the data caveat. Nothing is repeated from the schema and no sentence is 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?

With an output schema covering return values and annotations covering safety, the description supplies exactly the missing behavioral layer: the filter-consistency requirement, the not-found outcome, and the indicative-figures caveat. Nothing an agent needs to invoke this correctly on a 20-parameter tool is absent.

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 rises above that by defining the cross-call semantics of the filter parameters — they must be the same filters used on the list call, otherwise the plan is not found — which the schema alone does not convey. Remaining detail (callReason content, traveller counting, score thresholds) is fully handled by 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?

States a specific verb and resource ('Return one single-trip plan') and scopes it as singular against the list_travel_plans sibling, which is named explicitly. The mention of purchase_url and the filter-matching constraint further sharpens what the caller gets versus the list 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?

Establishes the operating context clearly: this is the single-plan retrieval that shares filters with list_travel_plans, so an agent knows to call it with a planCode obtained from a prior list. It gives no explicit when-not guidance (e.g., calling it without a planCode from a prior comparison), which is why it falls short of 5.

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