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

Beyond the annotations, it discloses pricing ($0.05 per call), the x402/MPP payment flow, that invalid input is refused before any charge, and the P0 key behavior (Authorization: Bearer p0k_, where to buy, price deducted). These are the kind of billing/auth details an agent cannot infer from readOnlyHint/idempotentHint.

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?

Front-loaded with the use case and alternative, then pricing/auth flow. Dense but nearly every sentence carries needed information; the long buy-key URL and payment mechanics make it longer than ideal but not padded.

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?

With no output schema, the description compensates by explaining the return payload (the exact x402 request, response schema, example) and what the agent must do with it. Auth, cost, and failure behavior are all covered, so an agent has everything needed to invoke and complete the call.

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 coverage is 100% and the schema already documents the 1–10 range and duplicate removal. The description's 'each answered exactly like /domain/report' adds slight semantic value about per-item output, but most parameter meaning lives in the schema, so baseline 3 is correct.

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?

States a specific verb and resource ('vet several domains at once'), gives the batch cap (up to 10 in one POST), and explicitly distinguishes from the single-domain sibling domain_report. An agent can tell exactly what it does and how it differs from domain_report.

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?

Opens with an explicit trigger ('Use when you must vet several domains at once (vendors, leads, lookalikes)') and names the alternative with its selection condition ('For one domain use domain_report'). Both when-to-use and when-not are present.

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