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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds a genuine behavioral caveat — data is returned 'publicly published ... as-is' — which warns the agent that fields may be redacted or missing; it does not mention registry coverage gaps or throttling, keeping it below a 5.

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 compact sentences: what it returns, the fidelity caveat, the intent triggers, and the cardinality constraint. Nothing is redundant and the resource definition is front-loaded.

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?

A read-only, one-parameter lookup with a full output schema and safety annotations leaves little for the description to carry. Scope, data fidelity, and intended queries are all covered; return values need not be explained because an output schema exists.

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% with a single well-documented parameter including examples ("acme.com", "8.8.8.8"). The description only reinforces the cardinality ('One target per call') and adds no syntax or format 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 and resource (WHOIS/RDAP registration data) plus the fields returned (registrar, status, creation/expiry, name servers) and the scope constraint (ONE domain or IP). An agent can distinguish it from dns_lookup or validate without opening either schema.

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 phrases — "who owns", "when does it expire", "registrar", "when was it registered" — which map user intent to this tool. It does not explicitly name the alternative (dns_lookup) or state when NOT to use it, so it falls short of full routing guidance.

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