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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds substantial context: minimum chargeable weight 0.5 kg, volumetric divisor L×W×H/5000, chargeable = max(actual, volumetric), 5–7 day transit, customs/VAT excluded, and a promo code that appears only for parcels ≥15 kg and never for documents. It even mandates a caveat the agent must relay (price confirmed after document check, with contact channels) — behavior that cannot be inferred from structured fields.

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?

Purpose and currency are front-loaded, then weight rules, then exclusions, then the mandatory caveat — a sensible order with no filler sentences. It is dense and slightly overloaded with promo/contact detail, but every sentence carries operational information.

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 no output schema, the description still tells the agent what the result means (price in UAH, customs excluded, promo code included for ≥15 kg parcels) and what caveat must accompany the answer. For a 7-parameter read-only calculator this is sufficient to call and present results correctly.

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 schema already documents each field, but the description goes further by explaining how the optional dimension parameters combine into chargeable weight and how sub-0.5 kg weights are rounded up — semantics the schema does not express. It does not add anything for direction or countryCode beyond what the schema states.

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+resource (estimated price of international express delivery) with concrete scope: to/from Ukraine, door-to-door, in UAH. It also pre-empts confusion with the customs sibling by explicitly excluding duty/VAT/clearance, so an agent can tell it apart from calculate_customs_payments without opening either schema.

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 explicit trigger phrasing ('Use when the user asks how much delivery costs / ціна, вартість... from or to a country') and defines applicability by weight band (documents up to 2 kg, parcels 0.1–70 kg, heavier on request). It stops short of naming the alternative tool for customs costs, relying on the exclusion sentence to imply that routing.

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