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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered; the description adds meaningful context beyond that by naming the underlying sources (ECHA harmonised list, Regulation 1272/2008, C&L Inventory, HSE, Korean GHS, US DOT 49 CFR 172.101) and by warning that mixtures require the user's own calculation. It does not describe coverage limits, staleness of the lists, or failure behavior when a substance is unmatched.

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 scope are front-loaded and no sentence is filler, but the prose is dense and list-heavy, and the UN number/transport concept appears twice (once in the opening clause, once in the transport clause), which slightly inflates the length for a single-parameter-required lookup.

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 five-parameter lookup with an output schema present, the description supplies everything an agent still needs: what sources are queried, what the optional flags add, which jurisdictions are supported, and what the tool deliberately does not cover. Nothing material 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?

Schema coverage is already 80%, yet the description adds real semantic value by mapping `jurisdictions` values to concrete data sources (EU CLP Annex VI, GB mandatory list/HSE, Korean GHS) and by tying `include_transport`, `include_notified` and `include_pending` to the specific datasets they pull in. The `substance` identifier formats are left to the schema.

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 ('looks up') and resource (a substance's GHS/CLP hazard classification, label elements and UN number), then enumerates exactly what comes back (Annex VI entry, H-statements, pictograms, signal word, SCLs, M-factors, ATP). It explicitly carves itself out from `regaffairs_check_chemical_substance`, so an agent can distinguish it from siblings without opening the 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 concrete triggers ('for SDS sections 2 and 3 or a CLP label', 'SDS section 14') and explicit when-not conditions: not for mixtures, not for ADR/IMDG/IATA rules, and restrictions go to `regaffairs_check_chemical_substance`. The only gap is that the positive trigger is embedded in the purpose sentence rather than framed as a standalone 'use this when' rule.

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