cart_add

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

Annotations already declare the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=true), so the description only needs to add context. It adds that the call returns the cart and that it is scoped to one-time purchases, but says nothing about how repeated calls behave (non-idempotent — does quantity accumulate?) or any auth requirements.

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?

Two short sentences, zero filler, with the core action and the purchase-mode constraint front-loaded. Nothing is redundant with the schema or annotations.

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 the description needn't document the returned cart. However, for a two-parameter mutation with 0% schema coverage, the description omits the one behavior an agent most needs (quantity accumulation semantics) and gives no indication of preconditions or failure modes.

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 0% and the description explains neither parameter. The critical ambiguity — whether 'quantity' adds to an existing cart line or replaces it, and what 'asin' must refer to — is left entirely unresolved by both the schema and the description, so the description fails to compensate 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 and resource ('Add a product to the cart') and clarifies scope with the one-time-purchase qualifier, which implicitly distinguishes it from a subscription flow. It does not, however, contrast itself with adjacent siblings such as cart, cart_remove, or checkout_request, so sibling differentiation is left to the name.

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 parenthetical 'one-time purchase, not Subscribe & Save' is a real exclusion that tells the agent when this tool is the wrong choice. But it names no alternative tool and gives no prerequisites (e.g., must the product be returnable/available), so guidance remains implied rather than actionable.

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