add_to_cart

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

No annotations are provided, so the description must carry the full behavioral transparency burden. It discloses the idempotent behavior (update quantity if part exists) which is helpful, but does not mention whether the cart_key must be valid or what happens on error. The description is adequate but not comprehensive for a mutation tool.

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 very concise: a title-like line followed by two brief sentences. Every sentence adds value—clarifying the action, the resource, and the edge case for existing parts. No wasted words.

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?

Given the presence of an output schema (not shown), the description does not need to explain return values. The tool has a clear, simple action, and the description covers the core behavior (add/update). A minor gap is authentication requirements or expected cart ownership, but overall it is sufficiently complete for the complexity level.

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 four parameters are already documented in the schema. The description adds no additional parameter-level detail beyond what the schema provides, so the 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?

The description clearly states the verb ('add') and resource ('item to existing shopping cart'), specifying exactly what action is performed. It distinguishes itself from update_cart_item by describing what happens when the part already exists in the cart (quantity updated), and is clearly not confused with get_cart or other siblings.

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 (an existing cart, a part number, and quantity). It does not explicitly state when not to use it or mention alternatives, but the sibling list provides natural contrast. The information is sufficient for correct invocation.

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