Update cart item

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

With no annotations, the description carries the behavioral burden. It clearly discloses that setting quantity to 0 removes the item, which is a non-obvious side effect. However, it does not mention error conditions, whether the quantity overwrites an existing value, or any authentication requirements beyond the implied 'authenticated user'.

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?

The description is a single, concise sentence that front-loads the core action and includes the most important edge case (quantity 0). No filler or redundancy.

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 simple two-parameter tool, the description covers the main intent and the removal edge case, but lacks information about failure modes, idempotency, or what happens when the item is not already in the cart. Given no annotations or output schema, a bit more context would be helpful, though the core usage is adequately clear.

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 100%, so the schema already documents both parameters. The description adds the 'authenticated user cart' context and reinforces the 0-removal behavior, but this largely mirrors the parameter descriptions rather than adding substantial new meaning.

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?

The description states a specific verb ('Set'), a clear resource ('item quantity in the authenticated user cart'), and a distinctive behavior (quantity 0 removes it). This cleanly separates it from sibling tools like add_to_cart and view_cart.

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 description implies usage context by mentioning 'authenticated user cart' and the update semantics, but it does not explicitly state when to prefer this tool over add_to_cart or view_cart, nor does it mention any exclusions or prerequisites beyond authentication.

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