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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false). The description does add genuinely non-obvious context: the response includes the merchant's encryption key for end-to-end encrypted order details. It does not mention any auth/permission requirements for retrieving that key, which is the most security-relevant behavior here.

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?

One dense sentence, front-loaded with the core action ('Full product card by sku'), followed by the field list. No padding, though the field enumeration partly overlaps the output schema.

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?

An output schema exists, so listing return fields is optional help rather than necessity. For a read-only tool with annotations covering safety, this is nearly adequate, but the absence of any auth/prerequisite note for a merchant-scoped, key-returning call leaves a real gap.

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 50%: merchant is documented as 'Merchant slug' while sku has no description. The description only adds 'by sku', clarifying that sku is the identifier, but says nothing about merchant format or how the two combine. Marginal compensation for the coverage gap.

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 ('Get a product card') and scopes it by lookup key ('by sku'), which implicitly distinguishes it from shop.catalog.search. It does not name a sibling explicitly, but the intent is unambiguous.

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?

No when-to-use guidance, no alternatives named, and no preconditions (e.g., must the merchant already be registered / terms accepted?). The 'by sku' phrasing implies a direct lookup, but nothing routes the agent between this and shop.catalog.search.

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