select_cart_items

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

With no annotations, the description carries the burden of disclosing behavior. It explicitly notes the writes_enabled gate, states that the tool modifies which items are ticked, and explains the return value (the cart after ticking). It also clarifies the effect on get_checkout. This is a solid disclosure, though it does not mention reversibility or idempotency.

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 a compact block of three sentences, each earning its place: the gate, the purpose/example, and the return behavior. It is slightly long but not wasteful, and front-loads the most critical information (the gate and the ordering dependency).

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 covers the essential context: the ordering flow, the dependency on get_checkout, and the return value. Given that an output schema exists (not shown here) and the input schema is fully descriptive, the description is complete enough for an agent to use the tool correctly. It does not over-explain.

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 schema already describes both parameters in detail (100% coverage), but the description adds a practical example ('buy these two' -> mode='only' with two skus) that clarifies the semantics beyond the schema. This adds value without redundancy.

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 a specific verb ('Choose') and resource ('cart items') and explains the tool's role as the step that composes a checkout. It clearly distinguishes this from read-only tools like get_cart and quantity-changing tools like set_cart_quantity, and ties it to the checkout flow.

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 explains when this tool is used ('the step that composes a checkout') and gives a concrete example of mode='only'. It implies that get_checkout depends on ticks, so this should be called before ordering. It does not explicitly name alternatives or state when not to use it, but the context is clear enough.

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