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

Goes well beyond the annotations: discloses pricing and payment rail (x402, USDC on Base), a partial-failure model ('A failed part is flagged (partial); fewer than 2 parts = not charged'), trial limits (3 per IP per UTC day), latency, and a privacy boundary (no personal contact data in RDAP). These are exactly the operational traits an agent needs and none are derivable 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-loads price, then the check inventory, then failure/billing terms — a sensible order for a paid tool. It is dense, with long parenthetical field lists, but nearly every clause (partial refund, latency, trial cap) carries decision-relevant 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?

An output schema exists, so return-value detail is unnecessary; the description instead covers cost, failure semantics, billing protection, and latency. For a 2-parameter, annotated, read-only aggregator, nothing an agent needs to invoke it correctly 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% and both parameters already carry descriptions, so the description rests at the baseline. It echoes the trial flag and does not add format detail for `domain` beyond the schema's 'a URL or email address also works'.

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 resource and scope with an enumerated contract: 'One call, one domain, four checks: DNS records..., RDAP registration..., email authentication..., TLS certificate basics...'. It also explicitly positions itself against siblings ('The core of dns-lookup + domain-rdap + email-auth + ssl-cert for the price of one call'), so an agent can tell exactly which other tools it replaces.

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?

Clear context for use: one domain, all four checks in a single call, with the sibling aggregation spelled out and a cost/latency rationale (~1-4 s, $0.002). It also routes to the trial path ('add "trial": true or use try_free'). It stops short of explicit exclusions, e.g. when to prefer the individual dns_lookup or ssl_cert for a single narrow check.

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