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

Annotations already declare this a non-read-only, destructive, idempotent write, and the description adds substantive context beyond them: the overwrite (not additive) semantics for the same itemId/configurationId, the append-when-absent behavior, standard pricing when wholesale is omitted, re-quoting of pricing/availability, the required cart:write scope, and that the updated cart view is returned. No behavioral gap is left for a mutation tool of this kind.

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 core action and overwrite semantics are front-loaded, followed by prerequisites, side effects and the sibling redirect. It is fairly long at seven sentences but each one carries a distinct fact; no sentence is redundant.

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 7-parameter mutation with no output schema, the definition covers everything needed: identity key semantics, overwrite vs append, auth scope (cart:write), prerequisite tool call, pricing re-quote side effect, and confirmation that the updated cart view is returned. Nothing an agent needs in order to call it correctly is missing.

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 baseline is 3, but the description adds real meaning the schema does not: the composite itemId/configurationId identity that determines overwrite vs append, and the default pricing behavior when wholesale is absent. It stops short of explaining return-value shape or the interaction among the three market codes.

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 (set cart line quantity and wholesale selection) and pins down the exact identity key (itemId/configurationId). It explicitly distinguishes itself from siblings by naming cart_remove_item and by clarifying it overwrites rather than adds, so an agent can tell it apart from cart_get, cart_clear and cart_remove_item without opening any 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?

Gives explicit when-to-use and when-not-to-use: call catalog_get_product first for supplier previews and use only configurations/buyer offers actually returned, use cart_remove_item to remove a line, and it names the condition under which a new line is appended. Alternatives and prerequisites are both spelled out.

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