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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely useful behavior beyond them: the exact record/certificate payload, the public-hosts-only scope limit, and the 0.005 USDC per-call cost with the accepted payment rails. It stops short of describing failure modes (NXDOMAIN, unreachable hosts, missing cert).

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?

Three tight sentences, front-loaded with the use case, then the return payload, then scope and cost. Every sentence carries distinct information; no 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?

With an output schema present the description needn't detail return values, yet it does so helpfully; annotations cover safety; and cost, payment rails and scope exclusions are all disclosed. An agent has everything needed to decide and 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?

Only one parameter and schema description coverage is 100% – the schema already specifies 'a hostname such as example.com (no URL, no IP address)'. The description adds only the constraint that hosts must be public, which is marginal over the schema, so the baseline 3 is appropriate.

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 (a domain's basic facts) and enumerates exactly what it returns: A/AAAA/MX/NS/TXT records plus the live TLS certificate with issuer, SANs, validity and days-to-expiry. No sibling tool performs domain lookups, so it is trivially distinguishable from the surrounding finance/crypto tools.

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?

'Use when an agent needs the basic facts about a domain' gives a clear trigger, and 'Public hosts only; no registrar data' carves out an explicit exclusion. There are no competing siblings to route against, so the absence of a named alternative is acceptable, but no prerequisite or edge-case guidance is offered.

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