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

Annotations declare readOnlyHint and openWorldHint, so the safety profile is covered, and the description adds genuine context beyond them: it identifies the data source ('public RDAP registry'), lists what an agent can expect, and explicitly discloses that registrant and contact details are not returned. This scope-limiting caveat is useful disclosure not present in structured fields.

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 action and data source, followed by the field list and the exclusion caveat. No redundant or filler text.

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?

There is no output schema, so the description compensates by naming the returned fields (dates, status codes, nameservers, DNSSEC, registrar). It is nearly complete for a single-param read-only lookup; only minor gaps like rate limits or response format remain.

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% with a single parameter, so the schema already documents the domain argument with a pattern and example. The description adds no format or syntax detail beyond what the schema provides, 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 ('Look up') and resource ('a domain') scoped to 'the public RDAP registry', then enumerates the returned data fields. This distinguishes it from siblings like dns_lookup and ens_resolve, which serve different resolution purposes.

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?

Usage context is implied by 'public RDAP registry' and the field list, but there is no explicit when-to-use guidance and no routing to alternatives such as dns_lookup or ens_resolve. The only boundary statement is the scope exclusion about registrant/contact details.

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