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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely non-obvious operational context: a per-call price of $0.002 USDC, the x402 payment rails (Base, Solana, Arc), and the fact that failed calls are not charged — exactly the kind of detail an agent needs before invoking a paid endpoint. Return shape is left to the output schema, which exists.

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 identity and returned fields are front-loaded in one dense clause, followed by input forms, the US-vs-UN caveat, and pricing. Every sentence carries information, though the parenthetical statute citation and the payment-rail list add bulk that could be tightened.

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 lookup with an output schema, the description covers what the tool returns, acceptable inputs, jurisdictional scope, and cost. The only missing piece is disambiguation from adjacent logistics hazardous-materials tools, which keeps it from being fully complete.

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 description coverage is 100%, so the single q parameter is already documented as a 4-digit UN number or a 3-to-60-character name fragment. The description restates the same two examples (1203, gasoline) without adding syntax, normalization, or matching-behavior detail, so it neither compensates nor detracts. Baseline 3 applies.

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 resource (US hazardous materials table, 49 CFR 172.101, eCFR) and enumerates the returned fields: UN number, proper shipping name, hazard class, packing group, labels, special provisions. It also pre-empts the most likely confusion by stating it is the US DOT table, not the UN list itself, which separates it from the other hazardous-goods 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?

Gives concrete input forms (a UN number like 1203, or a name fragment like gasoline) and a jurisdictional caveat about the UN Model Regulations, which implies usage. However, it never routes the agent against the close siblings such as logistics_hazardous_placard_id or logistics_lithium_battery_rules, and there is no when-not guidance.

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