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

With no annotations provided, the description carries the transparency burden. It clearly states that the tool initiates a $42 payment and returns a complete list of payment rails (card, USDC, BTC, x402, Zelle, invoice). It does not disclose prerequisites or failure handling, but the core financial action is explicit.

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?

Three sentences: action, output list, business rule. Front-loaded with the core verb and object, no redundant phrases. Every sentence adds information.

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 no annotations or output schema, the description lists all return values (Stripe card_uri, USDC uri, BTC uri, x402 POST /v1/sponsor, Zelle, GET /v1/invoice) and clarifies the settlement rule. This fully covers what an agent needs to know to call and interpret the tool.

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 input schema has zero parameters, so the schema conveys nothing. The description compensates by defining the fixed $42 amount and enumerating the return items, giving the agent complete semantic understanding of the no-input call.

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 action: 'Pay Fieldproof $42' with a specific amount and recipient. It also specifies what is returned (live rails with specific URIs), distinguishing it from sibling policy-check 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 clear context that this tool satisfies the first-$42 payment requirement ('One settlement meets the first-$42 bar') and returns payment rails. It does not explicitly list when not to use it, but the sibling tools are policy-related, so the usage intent is unambiguous.

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