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

With no annotations, the description carries the full burden and does reasonably well: it discloses the verdict scale and attached flags, the underlying signal sources, and the paid nature of the call (0.003 USDC via x402), which is behavior an agent must anticipate. It omits error behavior beyond the payment handshake, latency, and whether results are cached or rate-limited.

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?

Effectively three compact clauses: what signals are returned, what verdicts look like, what it costs. Front-loaded with the decision-relevant purpose and no filler. Slightly dense but every sentence carries 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?

No output schema exists, so the description must convey return shape, and it does: verdict enum plus flags plus the enumerated signal categories. Combined with a fully documented two-parameter schema, an agent has what it needs to call this correctly; only rate limits and failure modes are unaddressed.

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 both parameters are fully documented there, including the example domain and the complete 402/paymentProof retry flow, so the baseline is 3. The description's only added semantic is the price (0.003 USDC per call), which is useful but marginal relative to what the schema already explains.

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?

Names the resource (domain) and the deliverable (threat verdict: risk types, categories, popularity rank, URL-scanner verdicts, registration age) in the first clause, and states the return values (clean/suspicious/malicious with flags). It is clearly distinguishable from siblings like ip_reputation, whois, dns_lookup or url_parse, which cover different resources or different questions.

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?

Gives concrete trigger situations: before an agent visits a link, signs a transaction or pays an invoice. That is a clear positive-use context. It does not, however, say when to prefer this over ip_reputation or whois, nor when a verdict is unnecessary, so the routing guidance stops short of full discrimination.

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