now_add_items

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

With no annotations, the description carries the full burden and does disclose the critical side-effect boundary: 'Only changes the cart; never places an order,' which tells the agent this is not a purchase action. It also clarifies that quantity is additive rather than absolute, though it says nothing about partial-failure behavior or errors for stale ASINs.

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?

Three short sentences, front-loaded with the action, then prerequisites, then semantics, then the safety boundary. No filler or restatement of the tool name.

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 an unannotated mutation tool this covers the essentials: what it does, what each item must contain, how quantity composes, and that no order is placed. Remaining gaps—behavior on invalid/unknown ASINs and what the call returns—are modest since there is no output schema and no annotation contract to reconcile.

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 reported as 0% and the quantity property has no description at all, so the sentence 'quantity = units to add on top of what is already in the cart' resolves the most dangerous ambiguity (additive vs. absolute). The provenance rule tying searchQuery to the originating now_search query also adds meaning beyond the schema's bare 'The now_search query whose results included this ASIN.'

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 products to the Amazon Now cart') plus the batch scope ('several in one call'). The additive-quantity sentence implicitly separates it from now_set_cart_quantity, so an agent can choose between them 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?

Usage is conveyed indirectly: the requirement that each item carry 'the exact now_search query that returned it' implies search-then-add ordering. However, there is no explicit when-to-use/when-not statement or direct pointer to siblings like now_set_cart_quantity or now_view_cart.

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