Payment methods list

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

Beyond the readOnlyHint and idempotentHint annotations, the description adds a meaningful behavioral guarantee: full card numbers are never exposed to agents. This goes beyond the annotations and gives concrete safety expectations.

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 concise sentences with no fluff. It front-loads the primary purpose and then adds relevant behavioral detail. Every sentence earns its place.

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 provides sufficient context for the tool's purpose and behavior: it states what data is returned, the security constraint, and the relationship with purchase_confirm_intent. Given the simplicity of the operation, this is complete.

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 tool has zero parameters, so the baseline score is 4. The description does not need to describe parameters, and it does not add any parameter-related information. Since there are no parameters, no further explanation is required.

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 lists the principal's saved payment methods, specifies the returned data (last4 + brand), and explicitly notes that full card numbers are never exposed. This unambiguously distinguishes it from payment_methods_create and other related 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?

The description provides useful context by explaining how purchase_confirm_intent defaults when no payment_method_id is passed, implying when this list might be needed. However, it does not explicitly state 'use this tool when you need to present payment methods for selection' or otherwise give direct usage conditions relative to alternatives.

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