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

Annotations already cover read-only, idempotent, open-world, and non-destructive semantics, so the description focuses on substance: it discloses the data source (RDAP) and the returned fields. It does not mention rate limits, auth needs, or behavior for unregistered/privacy-protected domains, so it stops short of fully rich behavioral context.

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, front-loaded with the resource and return contents, then the routing pointer. Every clause earns its place with no redundancy.

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 usefully enumerates the key returned fields, and annotations carry the safety profile. It omits edge-case behavior (unregistered domains, WHOIS privacy redaction), which keeps it from being fully complete.

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 (domain) and schema coverage is 100%, so the schema already documents it fully with an example. The description adds no syntax or format detail beyond the schema, making the baseline 3 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 verb+resource (domain registration data via RDAP) and enumerates exactly what it returns (registrar, creation/expiration dates, domain age, nameservers). It even clarifies the RDAP-vs-legacy-WHOIS distinction and names the sibling dns_lookup as the contrasting tool.

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?

Explicitly routes the agent: 'For DNS records, use dns_lookup.' That is a concrete when-not condition naming the alternative, leaving no inference required.

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