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

Annotations already cover safety (readOnlyHint) and open-world scope, so the bar is low, but the description adds real operational context: the output includes dated CBP rules and presidential documents with numbers and links, and calls cost $0.002 USDC via x402 with failed calls not charged. The billing and payment-rail detail (Base, Solana, Arc) is exactly the kind of behavior an agent cannot infer from annotations or schema.

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 core is front-loaded, but the opening sentence is a long stack of parenthetical limit figures, and the trailing 'Related tools' sentence about an electric grid monitor consumes space without earning it. Billing information is useful but its placement after an irrelevant sibling reference buries the useful part.

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 present, the description does not need to enumerate return fields, yet it still summarizes what comes back (rules and presidential documents with dates, numbers, links). Combined with pricing and the optional value check, an agent has enough to invoke correctly; only the missing cross-reference to genuinely related customs tools holds it back.

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% for the single optional valueUsd parameter, so the baseline is 3. The description goes slightly beyond by explaining what the value is checked against — the $800 per person per day limit — and the $100 gift / $200 traveller limits, which gives the parameter regulatory meaning the schema alone does not.

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 names a specific regulatory program (US de minimis / Section 321) plus a concrete verb-like outcome: checking the $800 per person per day limit, current suspension status per Federal Register documents, and whether a shipment can enter duty-free today. This is clearly distinguishable from nearby logistics siblings such as logistics_customs_duty_calc or logistics_cross_border_ecom_vat.

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?

Usage is implied by the 'whether a shipment value can enter duty-free today' framing, which tells an agent the scenario it serves. However, there is no explicit when-not guidance and no routing to the relevant alternatives (customs duty calc, cross-border ecom VAT), while the one 'related tool' callout points to energy_us_electric_grid_monitor, which is irrelevant to this need and actively misdirects.

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