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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint, so the safety profile is established. The description adds valuable behavior beyond that: it resolves the compound, reports missing classifications gracefully, and notes the data is keyless and public-domain. It could mention ambiguity handling for name lookup, but overall it is transparent.

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 description is three sentences long, front-loaded with the core purpose, and every sentence earns its place. The input/output, graceful failure, source, and safety caveat are each covered without redundancy or 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 single-parameter read-only lookup with no output schema, the description is complete: it states what input to provide, what outputs to expect, how a missing classification is handled, and the limitations of the data. An agent has sufficient information to invoke the tool and interpret the result.

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%, and the schema already defines query as 'A chemical name (e.g. 'acetone', 'aspirin') or a numeric PubChem CID.' The description merely restates this input expectation. With full schema coverage, the baseline of 3 is appropriate; the description adds no new parameter-level detail.

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 opens with a specific verb and resource: 'Return the public GHS hazard classification for a chemical from the NIH/NLM PubChem database.' It goes beyond a vague statement by naming the exact output (signal word, hazard statements) and the accepted inputs (chemical name or PubChem CID). This level of specificity clearly differentiates it from generic sibling tools like chemical_lookup.

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?

The description gives clear context for when the tool is appropriate: when a GHS classification for a chemical is needed, using a name or CID. It also provides a useful exclusion—'not regulatory guidance or a safety data sheet'—and advises verifying against an SDS. However, it does not explicitly compare against sibling tools or name when an alternative should be preferred.

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