Check a substance against the SVHC Candidate List (EU)

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

No annotations are provided, so the description carries the full burden. It discloses the pricing behavior ($0.01/call, first call free), the billing-on-not-listed behavior, that results are dated to the served list, and the semantic caution that absence doesn't mean no concern. It doesn't discuss auth/rate limits but covers the meaningful behavioral nuances for this paid-check tool.

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 information-dense but front-loaded with the purpose statement, then delivers usage context and return-value specifics efficiently. The pricing/docs lines are slightly tangential for agent tool selection but earn their place given they're compliance-relevant billing signals. Structure flows purpose → usage → behavior → caveats.

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 lookup tool with 100% schema coverage, the description is thorough. It explains return semantics, obligations triggered, and caveats on the not-listed verdict. The absence of an output schema is compensated by the description's explanation of what's returned. Minor gap: no mention of response speed or failure/network behavior, but this is a well-covered single-query registry lookup.

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%, so baseline is 3. The description adds substantial value beyond the schema: it explains the mutual-exclusivity rule (exactly one key), the checksum validation, the 400 vs 200 response semantics, billing implications, and the UVCB special case where only name works. This meaningfully enriches the single-parameter 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?

The description is specific: 'Check a substance against the SVHC Candidate List (EU)' with clear verb+resource+scope. It specifies the query keys (CAS, EC number, exact name), what's returned (Article 57 inclusion reasons, inclusion date, EC decisions, triggered obligations), and distinguishes a 'not-listed' verdict from an all-clear. This clearly differentiates from sibling tools like label_chem_classify_batch and label_claims_check.

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 explicitly states when to use this tool ('Before your agent clears a substance, an article or a supply-chain declaration for the EU market'), naming the concrete workflow trigger. It frames the purpose against the ECHA/REACH compliance context, and the parameter guidance specifies exactly one key among cas/ec/name with error semantics, distinguishing from batch siblings.

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