Add or set a product in the cart

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

With no annotations provided, the description carries full burden. It discloses the mutative action (set quantity), the add-if-absent behavior, and the prerequisite condition. It could additionally mention idempotency or effects on other cart items, but overall it is transparent.

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?

Three concise sentences with no wasted words. The first sentence front-loads the core purpose, followed by input sourcing and prerequisites. Every sentence 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?

Given no output schema and only two parameters, the description covers purpose, prerequisites, failure mode, and input sourcing. It does not mention return behavior, but that is not critical for this simple tool. Nearly 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 coverage is 100%, so baseline is 3. The description adds meaning by specifying that 'slug' must come from 'search_products' and that 'quantity' is the value to set (not merely add), going beyond the schema descriptions.

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 'Set' and resource 'quantity of one product in the cart' with the added detail that it adds the product if absent. It distinguishes itself from sibling tools like 'add_many_to_cart' and 'remove_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?

Explicitly mentions that the tool accepts a product slug from 'search_products' and requires sign-in and an existing cart, with a prerequisite call to 'set_delivery_slot'. It also warns of a specific failure condition (404 error), providing clear when-to-use and when-not-to-use guidance.

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