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

Annotations already declare readOnlyHint=true and idempotentHint=true, covering the safety profile. The description adds meaningful behavioral detail by explaining the meaning of fields such as retail being per-day when daily_unlimited is true, location_codes representing covered countries, and id being the plan_id for an order.

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?

The description is dense and mostly efficient, front-loading the core purpose and then listing the return fields. The field list is presented as a long single sentence with several parenthetical clarifications, which is slightly cumbersome but still compact and free of filler.

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 one-parameter, read-only, idempotent tool with an output schema, the description covers the essential context: how to obtain the slug, what fields are returned, and specific unit semantics for retail. It does not discuss error behavior or the broader purchase flow, but those are less critical given the annotations and output schema.

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?

The schema only says 'Slug' with no description, so the 0% schema coverage puts the burden on the tool description. The description compensates by explaining that slug identifies one destination and that it should come from search_destinations, which is the key semantic an agent needs.

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 clearly identifies the resource (plans) and scope (one destination, identified by slug), and it points to search_destinations as the slug source. It lacks an explicit action verb like 'retrieves' or 'lists', and it does not contrast itself with sibling tools, but the intent is unambiguous.

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 phrase 'slug from search_destinations' gives clear prerequisite context: call search_destinations first to obtain a destination slug, then use this tool. It does not explicitly state when not to use this tool or name alternatives, so it falls short of full explicit routing guidance.

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