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

The description adds useful behavioral context beyond the annotations: it returns cart_id, cart contents, and a customer link, and it explicitly states that nothing is charged. This partially compensates for the absence of an output schema and for the tool being a mutating operation without an idempotency guarantee.

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 short sentences cover the action, the inputs, the return values, and the key non-side-effect. Every sentence adds value and the most important information is front-loaded.

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?

The description is reasonably complete for a simple cart-building tool: it defines inputs, outputs, and the important 'does not pay' boundary. It does not describe error cases or idempotency, but those are less critical given the simple two-parameter schema and the provided return summary.

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?

The main parameter, items, has no schema description, but the tool description explains exactly what it expects: a list of variant_id and quantity pairs. The optional cart_id has its own schema description ('Add to existing cart'), so combined coverage is adequate.

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 states the specific verb and resource: assembling a cart from a list of executions (variant_id + quantity). It also clearly distinguishes the tool from order creation by noting that it does not pay for anything and instead returns a buyer-facing cart link.

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 makes the core usage clear: build a cart from variant/quantity pairs and get a shareable link. It does not explicitly name sibling alternatives like create_invoice_order or suggest_accessories_for_cart, but the 'does not pay' note helps an agent decide between cart building and order/invoice creation.

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