Set Default Payment Method

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

No annotations are provided, so the description carries the full burden of disclosing behavioral details. It only states the action ('Set a payment method as the default') without revealing any side effects, requirements, reversibility, or error behavior. For a mutation tool with no annotation coverage, this is a significant gap—it does not tell the agent what happens after the operation or any special conditions.

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 single, front-loaded sentence: 'Set a payment method as the default.' Every word is necessary and there is no fluff. It is appropriately concise for such a simple tool.

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 tool is simple with one parameter and no output schema, but the description still lacks useful context: what it means to be the 'default' (e.g., for renewals or purchases), any prerequisites, or what the return value/response will be. While the core function is clear, the missing context could lead to an agent using it without understanding the broader billing implications.

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% (payment_method_id is described as 'Payment method ID'). The description adds no extra parameter semantics beyond what the schema already provides. Since the schema covers the only parameter, the baseline of 3 applies.

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 uses a specific verb ('Set') and clearly indicates the resource ('a payment method') and the resulting state ('as the default'). This clearly differentiates it from sibling billing tools like billing_delete_payment_method, billing_get_payment_methods, and billing_enable_auto_renewal, which focus on different operations.

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: when you want to set a payment method as the default, use this tool. However, it does not provide explicit guidance on prerequisites (e.g., that the payment method must already exist), nor does it compare with alternatives. The usage is clear from the tool's name and direct statement, but no explicit when-to-use or exclusions are given.

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