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

With no annotations, the description carries the burden well: it discloses rate limiting, a ~5s timeout, SSRF safety (no private redirects), input rejection rules, and even cost ($0.003 via x402). It stops short of describing failure/error behavior or response shape beyond the field list, which keeps it from 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?

A single dense paragraph with the core purpose front-loaded and every clause carrying information (scope, exclusions, rate limit, timeout, safety, price). No filler or restated title.

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?

For a two-parameter read-only lookup with no output schema, the description covers scope, exclusions, limits, safety, and cost, and enumerates returned fields. Only error/failure semantics are 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?

Schema coverage is 100%, so both the domain and request_id parameters are already documented in the schema, including the idempotency semantics. The description adds only the IP-literal rejection constraint on domain, 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+resource ("Domain registration lookup via IANA RDAP DNS bootstrap only") and enumerates the data returned (registrar, status, nameservers, events). It doesn't name siblings like dns_lookup or name_resolve explicitly, but "registration" vs "DNS lookup" makes the distinction inferable.

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?

It defines negative scope clearly ("Rejects IP literals and private names", "RDAP bootstrap only"), which implicitly steers callers away from misuse. However, there is no explicit when-to-use-this-vs-alternative guidance for siblings such as dns_lookup or name_resolve.

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