Create Checkout Session

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

With no annotations provided, the description carries the behavioral burden. It discloses a key side effect — 'Clears any existing cart and starts a new checkout session' — and describes the return fields. It does not cover error conditions or authorization requirements, but the material behavior an agent needs is present.

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 well-structured with Args, Returns, and an Example. Every sentence contributes: purpose, when to use, side effect, return value relevance, parameter details, and a concrete invocation example — no filler or redundancy.

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 single-parameter tool with no annotations and an opaque input schema, the description provides the item structure, defaults, source of valid product IDs, and return fields. The example makes the expected call unambiguous, leaving no missing information needed to invoke it correctly.

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 0% and the schema only defines items as an array of objects with additionalProperties true. The description fully compensates by specifying each item's product_id type, its source list_shop_products, and the optional quantity defaulting to 1, adding significant meaning beyond the schema.

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 action — 'Create a UCP checkout session' — with a clear scope ('one or more products'), and differentiates itself by noting that the returned session_id is required for subsequent update and complete calls, which distinguishes it from sibling checkout tools.

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?

It explicitly says 'Use this when the user wants to buy something' and tells the agent to source product_id from list_shop_products. It implies the workflow order by referencing subsequent update and complete calls, though it does not explicitly state when not to use it or compare it to cancel_checkout_session.

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