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

Annotations already declare readOnly, idempotent, closed-world, non-destructive, so safety needs no restating. The description adds genuinely non-structured context: the dataset covers only 157 UN numbers and only liquids, and the ambiguity behavior of name lookups is disclosed. It does not mention latency or any failure/empty-result behavior.

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, front-loaded with the action and source, then the payload, then the edge case. Zero filler; every sentence carries information an agent needs before calling.

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?

No output schema exists, so the description carries the return-value burden and discharges it by listing the returned fields and the per-container allowed codes and size. The dataset's coverage boundary (157 liquids) and the ambiguous-name path are both stated, leaving nothing essential missing for a 2-optional-param read tool.

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% with format examples for both params, so the baseline is 3. The description earns above that by explaining the interaction between un and name: name may map to several entries, in which case candidate UN numbers come back and un must be supplied.

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?

Specific verb and resource: look up a UN number or substance name in ADR 2025 Table A plus its packing instructions. It goes further and enumerates what is returned (class, packing group, limited quantity, UN mark level, per-container UN codes and max litres), so an agent can distinguish it from decode_un_packaging_mark without opening any 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 follow-up guidance: an ambiguous substance name returns candidate UN numbers and you must call again with un= set to one of them. It does not, however, name a sibling alternative or say when to prefer decode_un_packaging_mark or jerry_can_quantity instead, so routing guidance is partial.

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