Set the exact quantity of an item already in the Amazon Now cart; set it to 0 to remove the item.
Set the exact quantity of an item already in the Amazon Now cart; 0 removes it.
| Name | Required | Description | Default |
|---|---|---|---|
| asin | Yes | Amazon product ASIN, from now_search results. | |
| quantity | Yes | Target quantity; 0 removes the item. |
Changes observed during successful MCP inspections.
v0.2.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations exist, so the description carries the burden. It correctly signals a mutating operation and usefully discloses that quantity 0 deletes the entry, but says nothing about permission/auth needs, what happens if the ASIN is absent from the cart, or whether totals are recalculated.
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 short sentence, verb first, with the destructive edge case (0 removes) attached immediately. Nothing is padded or restated.
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 a two-parameter mutation with no annotations and no output schema, the definition covers the core action and the deletion edge case but leaves error behavior and post-call state unstated. Adequate but with visible gaps.
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%: the asin pattern and its origin ('from now_search') and the quantity 0-20 range with the 0-removes meaning are all documented in the schema. The description's mention of 0 removal merely repeats the schema, adding no new parameter semantics; 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 ('Set') and resource ('exact quantity of an item') plus the scope constraint 'already in the Amazon Now cart', which implicitly separates it from now_add_items and now_view_cart. It stops short of naming a sibling explicitly, so sibling differentiation is inferred rather than declared.
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?
'0 removes it' and 'already in the cart' imply the use case and one edge case, but there is no statement of when to prefer this over now_add_items or now_view_cart, nor what to do if the item is not yet in the cart. Usage is implied, not instructed.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.