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

With no annotations, the description carries the full burden, and it delivers the two facts an agent most needs operationally: a rate limit (5 free calls/day across all tools) and a cost model (pass `key` for a 0.005 USDC prepaid balance). It does not say what happens on a nonexistent or invalid domain, so error behavior remains undisclosed.

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 sentences, front-loaded with what is returned, then when to use it, then the cost constraint. The field enumeration is long but each item is informative; nothing is redundant padding.

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 and no annotations, the description compensates by enumerating the returned fields and stating the pricing/rate-limit model. The only meaningful gap is failure semantics for bad or unregistered domains, which an agent would want before relying on the result.

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% for both parameters, so the baseline is 3. The description adds only marginal value, clarifying that `key` draws on a prepaid balance, while `domain` semantics are left entirely to the schema.

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?

The description names the specific resource (RDAP domain registration data) and enumerates the returned fields — registrar, dates, age, status flags, nameservers, DNSSEC — which is far more specific than the tool name alone. It never names a sibling, so an agent must infer on its own that this differs from check_domain or tls_certificate, which keeps it short of a 5.

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?

"Use it to spot a newly registered or soon-to-expire domain" gives a concrete decision context for invoking the tool. It stops short of explicit exclusions or naming the alternative (check_domain for availability), so it is clear context without routing guidance.

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