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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety and external-lookup behavior are covered. The description adds genuinely new information beyond the annotations: the quota model ('every 3 domains with a registry answer count as one result, rounded up per request') and the availability check, both of which affect how an agent batches calls.

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?

The result fields are front-loaded in one dense sentence, followed by the cost/batching rule. Every clause earns its place, though the long enumeration makes the first sentence slightly heavy.

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, and it covers the batching/cost rule for a tool that accepts up to 50 domains. Nothing critical to invoking 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 description coverage is 100% (both parameters documented, including the 1-50 range and the default-true includeDns flag), so the schema carries the parameter burden. The description restates the record types that includeDns controls but adds no format/syntax detail beyond the schema, so baseline 3 applies.

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 (look up) and resource (domain registration/DNS records), then enumerates the exact fields returned (registrar, creation/expiry dates, status, nameservers, DNSSEC, A/MX/SPF/DMARC, availability). An agent can distinguish this from every sibling tool, none of which touch DNS or WHOIS.

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?

The description makes the domain-lookup context obvious but never states when to use this versus an alternative, nor any exclusions or prerequisites. Sibling tools are in unrelated domains, so implied usage is reasonably clear, but there is no explicit guidance.

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