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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It only states that the tool modifies cart items and "maintains cart integrity during updates," which is vague. It does not disclose behavior on invalid line_item_id, whether quantities are set absolutely or incremented, side effects, reversibility, or required auth. For a mutation tool, this is a significant gap.

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 structured with clear sections: intro, use cases, features, flow, and prerequisite. It uses bullets for readability. However, it has some redundancy (first two sentences both state the purpose) and a typo ("updatem"), and the feature bullet "Maintains cart integrity during updates" is vague. Overall, it is appropriately sized but could be tightened.

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?

The tool has a complex nested schema for selectedOptions, and the description provides a high-level overview of use cases but lacks detail on parameter semantics. The flow section helps by directing users to get_product_details for product variants, which is useful. However, it omits error scenarios, partial update behavior, and response details (though an output schema exists). For a mutation tool with this complexity, the description is only partially complete.

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%, so the description must compensate. It does add some meaning by mentioning quantity adjustments, product variants, and custom properties, which map roughly to the 'item' object's quantity, variantEntityId, and selectedOptions. However, it does not explain how to structure the selectedOptions object or whether productEntityId can be changed. line_item_id is not explicitly defined, though its purpose is implied by the name.

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 clearly states the tool's purpose: "Modify existing items in your shopping cart." It uses a specific verb (modify) and resource (cart items), and explicitly lists concrete operations like changing quantities, updating product variants, and modifying custom properties. This distinguishes it from sibling tools like add_item_to_cart and remove_item_from_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 provides explicit use cases with "Use this tool when customers need to..." and a step-by-step flow that references sibling tools. It also mentions a prerequisite ("Requires an existing cart with items to modify"). However, it does not explicitly state when NOT to use this tool vs alternatives like remove_item_from_cart, though the use cases make that clear.

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