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

Annotations already declare readOnly, idempotent, and non-destructive, and the description reinforces that with "Places no order and charges nothing" plus the fact that a price estimate is returned. It adds a genuinely new behavioral constraint not present in the schema: only single-country scope is validated against the itinerary.

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 sentences ordered as trigger, checks performed, and side-effect guarantees. Every clause carries information an agent needs, and the most decision-relevant content (when to use, no charge) is front- and back-loaded for scanning.

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?

Output schema covers the price estimate, annotations cover the safety profile, and the schema fully documents all four parameters. The description fills the remaining gap by explaining the validation rules and the no-charge guarantee, leaving nothing an agent needs before calling.

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 the baseline is 3, but the description goes further by explaining what each parameter is used for in the check: quantity validated within 1-50, device_model drives a compatibility check, and countries is specifically for scope validation rather than, say, pricing.

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 (verify/validate) and enumerates exactly what is checked: plan id existence, quantity bounds, eSIM compatibility, and country scope, then that it returns a price estimate. It also positions itself as the pre-purchase dry run, which separates it from siblings like compare_plans and get_plan_details.

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?

"Use when the user is about to buy and wants everything checked first" gives a clear activation condition tied to purchase intent. It does not explicitly name an alternative or an exclusion (e.g., when to skip validation and go straight to ordering), which keeps it 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.