Add checkout payment (get payment URL)

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

With no annotations, the description carries the burden of disclosing side effects and returns. It does state return values (checkout URL + session id) and the timing of the transaction id. However, it omits important behavioral details such as fund holding vs. immediate charge (though the use_hold parameter schema covers this), permission requirements, or any side effects beyond adding a payment. This is adequate but not rich.

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 two sentences, front-loaded with the core function, and every clause adds information. No fluff or redundant wording.

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?

Despite having 7 parameters, nested objects, and no output schema, the description plus schema cover the essential context: what the tool does, prerequisites (existing session), and return values. It could mention the need to ask about hold vs. charge, but that is already in the use_hold schema description. Overall, adequate for the complexity.

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%, so the baseline is 3. The description itself adds no parameter-specific meaning; it relies entirely on the schema, which already documents each parameter well, including the critical use_hold business decision.

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 clearly states the tool's function: 'Add a payment to an existing checkout session' with a specific verb and resource. It also differentiates it from creating a session (create_checkout_session) and status retrieval (get_session_status) by noting the return of the checkout URL and session id, and pointing to later transaction id availability.

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 implies usage context: it requires an existing checkout session (as opposed to creating one) and coordinates with get_session_status for the transaction id. However, it does not explicitly name alternative tools like add_acquiring_payment or state when not to use this tool, so guidance is clear but not exhaustive.

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