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

Annotations already declare this a non-destructive write in a closed world, so the bar is lower. The description adds genuine constraint context the annotations do not carry: a per-item cap of 10 and a cart total of 50, which shapes how an agent should batch adds. It omits what happens when the cap is exceeded.

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 tight sentences with zero filler. The primary action is front-loaded and the constraint sentence follows, so an agent gets the operation first and the limits second.

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 mutation tool with no output schema and annotations carrying the safety profile, this covers action, variant handling, and quantity caps adequately. Missing only error behavior on cap violation and explicit sibling routing, which are minor given the surrounding schemas and tools.

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?

With only 50% schema description coverage, the description must compensate, and it does partially: it explains the combination concept ('products with sizes or colours') and the quantity limit that reinforces the schema's maximum: 10. cart_token and product_id semantics remain undocumented in both places.

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?

Clear verb+resource: 'Adds a quantity of a product ... to the cart', which an agent can distinguish from set_quantity and remove_line. It also clarifies the combination case for sized/coloured products. It stops short of explicitly naming a sibling, so it is clear but not routed.

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?

Usage is only implied by the verb 'adds' plus the stated caps ('at most 10 of one item and 50 in total'). There is no explicit when-to-use-vs-alternatives guidance (e.g. add_line vs set_quantity), nor any statement about prerequisites beyond the cart_token reference.

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