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

Although annotations already declare readOnly/idempotent/non-destructive/openWorld, the description adds substantial behavior the annotations cannot express: exact price ($0.015 per call), the x402/MPP payment flow, the two distinct operating modes, the auth header format for the P0 key, and the guarantee that 'Bad input is refused before any charge.' That is precisely the cost/authorization context an agent needs before invoking a paid, open-world tool.

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?

Usage condition is front-loaded, followed by return behavior, then pricing and the P0-key shortcut — a sensible order with little redundancy. The third sentence is dense and carries a long embedded URL, but that URL is operationally required rather than filler.

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 paid, open-world aggregator with no output schema, the description covers what an agent must know before calling: price, payment mechanics, auth requirements, return shape (a paid request plus a schema link), and input validation. Nothing essential to a correct invocation is missing.

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%, so the baseline is 3; the description earns above that by expanding what each input type actually returns (ip → ASN/Tor exit/cloud range; domain → status/TLS/robots; cve → CVSS/EPSS/CISA KEV), which the schema does not say. It does not clarify whether multiple inputs can be supplied at once or what the mutual-exclusivity rule is, which is the one semantic gap.

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 opens with a specific verb ('check') and enumerates the resource classes it covers (ip/asn/tor/cloud range, domain/status/TLS/robots, cve/CVSS/EPSS/KEV), plus the underlying endpoint GET /check/infra. The phrase 'in one call' implicitly separates it from the narrower siblings (ip_passport, domain_report, vuln_cve), but none of them are named, so an agent must infer the routing rule.

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?

It gives a clear use condition — 'Use when you must check infrastructure in one call' — which contrasts with the single-purpose siblings, and it explains the two invocation modes (retrieve the x402 request vs. let the tool pay with a P0 key). It never states when NOT to use it, e.g. when a deeper single-domain report is wanted, so routing is left partly to inference.

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