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

Annotations already cover read-only, idempotent, non-destructive, open-world, so the remaining burden is low. The description adds genuinely non-obvious behavior: a $0.01 USDC charge per successful call via x402 on Solana, plus an equivalent HTTPS endpoint — details an agent cannot infer from any structured field. It stops short of stating failure/charges behavior or expected latency.

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, both front-loaded: capability inventory first, then the operational caveats (use case, price, transport). No filler or restatement of the title, and the signal list is dense rather than 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 correctly enumerates what comes back (registration dates, record types, cert issuer/expiry/SANs/trust, subdomains, risk flags), which is what an agent needs to decide whether one call suffices. The cost model is disclosed, but edge behavior (invalid domain, upstream failure, whether a failed call is billed) is not.

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?

Single parameter with 100% schema description coverage ('Registrable domain, e.g. example.com'), so the schema carries the load and the baseline is met. The description adds no input detail and leaves one real ambiguity unaddressed — whether a subdomain can be passed given that CT subdomain enumeration is part of the payload.

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+resource ('One-call domain due-diligence') and enumerates exactly which signals are combined: RDAP age/expiry/registrar, DNS record types, live TLS cert, CT subdomains, and risk flags. This clearly positions it as an aggregator distinct from narrow siblings like rdap_age, dns_dump, ssl_cert_info, and ct_subdomains.

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 an explicit use case: 'phishing/scam triage of links before an agent visits or pays them,' which tells the agent the moment to reach for it. It does not name when to prefer the cheaper single-signal siblings (rdap_age, ct_subdomains, phishing_score) instead, so the alternative-selection guidance is implied by 'one-call' rather than stated.

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