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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses commercial behavior that structured fields do not: $0.002 USDC per successful call via x402 on Base/Solana/Arc, and that failed calls are not charged. It also discloses data coverage gaps (no CIR safety assessments). It does not mention rate limits or result ordering, keeping it short of a 5.

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?

Front-loaded with the core purpose and returned fields, then exclusions, alternatives, and cost in a sensible order. Minor waste: the title fragment 'INCI name' is repeated, and the single long sentence chain plus pricing clause makes it denser than necessary.

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?

With an output schema present, return values need not be enumerated, yet the description still summarizes them; scope, source, exclusions, sibling routing, and pricing are all covered. The only gap is that matching behavior for common vs. INCI names (partial matches, synonyms) is not described.

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 both 'name' and 'limit' are already documented in the schema (including the 1-25 range and default of 10). The description adds no additional parameter meaning beyond repeating that lookup is by INCI name. 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?

States a specific verb and resource ('Cosmetic ingredient lookup by INCI name') plus the exact fields returned (cosmetic functions, chemical description, CAS/EC numbers, CosIng ID) and the authoritative source (EU CosIng inventory). This is enough to distinguish it from health_eu_cosing_cosmetics without opening either 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?

Explicitly names scope limits ('CIR safety assessments ... are not included; use eu-cosing-cosmetics for EU restrictions') and routes to the named sibling 'health_eu_cosing_cosmetics when you need EU cosmetics regulatory status for a substance name'. Clear when-not and alternatives are both present.

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