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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds one genuinely new behavioral fact — 'Free public API', implying no authentication or quota credential is needed — but says nothing about rate limits, behavior for non-existent or privacy-shielded domains, or latency of an external call.

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 compact sentences, front-loaded with the access model then the verb and resource, with the returned field list carrying real 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?

Output schema exists and annotations are rich, so return values and safety need no restating. For a single-param external lookup the description is nearly sufficient; only edge-case behavior (invalid/nonexistent domain, rate limiting) is unaddressed.

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?

With a single required parameter at 100% schema description coverage, the schema itself fully documents 'domain'. The description only restates the resource ('for a domain') and adds no format hints (TLD handling, IDN, subdomain acceptance), so 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 verb (lookup) and resource (WHOIS/RDAP record for a domain) and enumerates the returned data categories (registrar, status, dates, nameservers). This differentiates it cleanly from siblings like tools_dns_record_lookup, tools_domain_availability_checker, and tools_domain_age_checker without opening a 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?

No when-to-use guidance, no exclusions, and no mention of alternatives among the 17 sibling domain/DNS tools. The agent must infer that this is for registration metadata versus DNS resolution or availability.

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