Complete Checkout

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

With no annotations, the description carries the burden of behavior disclosure. It does reveal that the tool finalizes/submits the order and that the returned payment_url must be opened by the user to pay via PostFinance Checkout, which is useful. However, it does not state whether this action is irreversible, whether the session becomes invalid, or what side effects occur beyond returning the URL.

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 only three short sentences, front-loads the primary action, and adds relevant context about the payment flow. Minor repetition of 'return the payment URL' and 'Returns a payment_url' is not wasteful because the second instance adds the important browser/payment-provider detail.

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 one-parameter tool with an output schema, the description covers the purpose, the correct timing, and the nature of the output well. It could more explicitly warn that calling complete_checkout ends the editable checkout phase, but 'finalise the purchase' implies this sufficiently.

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 description coverage is 100%, and the schema already explains session_id as coming from create_checkout_session. The description does not add meaning to the parameter, but with full schema coverage this is an acceptable baseline.

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 names the specific action ('Submit the order') and the key output ('payment URL'), and clearly positions the tool as the finalization step after update_checkout_session. This distinguishes it from its sibling checkout tools without requiring schema inspection.

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 states when to use it: 'Use this after update_checkout_session to finalise the purchase.' This gives clear sequencing relative to a sibling tool. It does not enumerate exclusions or mention cancel_checkout_session, but the intended position in the flow is unambiguous.

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