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

Annotations only declare readOnlyHint and openWorldHint, but the description adds material context: the authoritative source (ICC 'ATA Carnet in your country' page), the pricing model ($0.002 USDC per successful call via x402 on Base, Solana or Arc), and that failed calls are not charged. That cost-and-failure disclosure is exactly the kind of behavioral detail an agent needs before invoking.

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 is front-loaded in the first clause, followed by source, limitation, and pricing in descending priority. The second sentence is dense (limitation, price, payment rails, failure policy all in one), but no sentence is 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 lookup with an output schema already defining the return shape, the description covers the remaining gaps: data provenance, the public-verification limitation, and payment terms. Nothing an agent needs to decide or pay correctly is missing.

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?

Single parameter with 100% schema description coverage, so the schema already documents accepted forms (country name or two-letter code, with examples). The description adds no additional input semantics, which is acceptable at this coverage level but yields only the baseline.

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?

Names a specific verb+resource: checking whether a country participates in the ATA Carnet system, and returns its national issuing/guaranteeing association with contact details. The parenthetical defining ATA Carnet (duty-free temporary admission for samples, professional equipment, exhibition goods) and the ICC source make the scope unmistakable and distinguishable from the tariff/customs siblings.

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?

Explicitly bounds the tool by stating that individual carnet numbers cannot be verified publicly and that the association answers those queries, which steers agents away from a plausible misuse. It stops short of naming a sibling alternative or stating the positive trigger conditions (e.g., pre-shipment planning) more concretely.

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