Test the payment stack end-to-end (paid via x402, $0.001)

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

With no annotations, the description carries the burden of disclosing behavior. It states the cost ($0.001), the fact that it's a real purchase, that failures are never billed, and the return value (payer + network). This covers key behavioral traits, though it omits potential side effects like transaction logs or idempotency.

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?

Two sentences, front-loaded with the core purpose, and no wasted words. It includes return values and failure billing in a compact manner.

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 zero-parameter tool with no output schema, the description is complete: it covers what it does, why to use it, cost, success/failure behavior, and return fields. No additional context is needed.

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, and the schema coverage is 100% (empty). The description does not need to explain parameters, and the baseline for a no-parameter tool is 4. It provides no misleading parameter information.

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 states a specific action ('test the payment stack end-to-end') with a clear resource (x402, production seller) and distinguishes itself from siblings by emphasizing it's the cheapest possible real purchase. It also clarifies its role as a pre-flight check before expensive 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 phrase 'before you point it at anything expensive' clearly indicates when to use the tool. It does not name explicit alternatives or exclusions, but the context is sufficient for an agent to choose it as a preliminary payment test.

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