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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the mutation/destructive profile is covered structurally. The description adds the non-obvious rule that quantity <= 0 deletes the line (though the schema repeats this), but says nothing about whether omitted optional fields are preserved or overwritten, nor about required auth.

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 with zero filler, and the destructive quantity rule is front-loaded alongside the primary purpose. Every clause earns its place.

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 and the input schema is fully described, so the description does not need to explain returns or parameter formats. The remaining meaningful gap is the overlap with cart_remove_item and the replace-vs-preserve behavior for omitted optional fields.

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 all five parameters are already documented in the schema, including 'Use 0 to remove' and the replacement semantics for notes and selectedOptionIds. The description only restates the field list and adds no syntax, format, or default-behavior detail beyond it.

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+resource (update quantity, notes, or selected options on an existing cart line item) and includes the removal side-effect. It does not differentiate from the sibling cart_remove_item, which reaches the same end state via quantity <= 0, leaving a routing ambiguity.

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?

No explicit when-to-use guidance and no alternatives named. The only usage signal is the inline 'Quantity <= 0 removes the item', which competes with the dedicated cart_remove_item sibling without saying which path to prefer or what preconditions exist.

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