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

Annotations cover safety (readOnlyHint, openWorldHint), and the description adds real value beyond them: it discloses that quantities are live and change between calls, and that unrecognized part numbers surface in not_found rather than failing the whole call. It doesn't state rate limits or partial-failure handling for mixed valid/invalid inputs.

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 is front-loaded in the first clause and each sentence carries distinct information (fields, differentiation, liveness, error case). The boolean example ('36 units' vs '84,386 units') is illustrative but slightly verbose for the value it adds.

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?

Output schema exists, so the return-field enumeration is somewhat redundant, but the description usefully adds the error path (not_found), the liveness caveat, and the scope cap. For a single-param read tool this is complete enough; only minor gaps remain around batch failure semantics.

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 the schema already documents part_numbers, the comma-separated format, the 20-item cap, and cross-references to chewy_product/chewy_category. The description only restates 'keyed by part number' and 'up to 20', adding no new syntax or format detail beyond the schema, so the 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+resource: returning Chewy's live warehouse inventory position keyed by part number, with enumerated fields. It also explicitly distinguishes itself from siblings by noting it is 'the only Chewy surface carrying real quantities' while other endpoints are boolean-only.

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 boolean-contrast sentence tells the agent exactly when this tool is the required choice over other Chewy endpoints. However, it names no specific sibling tool and gives no explicit when-not-to-use exclusion, so it falls short of a 5.

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