Look up domain WHOIS

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

Annotations already cover the safety profile (readOnly, non-destructive, open world), and the description adds substantial behavior: exact cost model (10 credits fresh, 0 on cache reuse), separate provider billing, synchronous result with no job ID, no inference of missing/redacted fields, and a prompt-injection warning that WHOIS data is untrusted content.

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?

It is front-loaded with purpose and return scope, then layers cost and safety notes. There is minor redundancy: the 10-credit/zero-cache cost is stated in both the description and the forceLive schema field, and the 'MCP admission units are separate from provider credits' restates the prior billing sentence.

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 must convey return contents; it lists the fields returned (registration, registrar, dates, nameservers, contact/server/social) and clarifies synchronous delivery plus balance reporting. This is adequate, though the exact response shape remains unspecified.

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%, so the baseline is 3. The description reiterates the fresh-vs-cache cost that the forceLive schema already states, and adds no syntax or normalization detail beyond what the schema documents for domain and source.

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 states a specific verb and resource ('Look up domain registration, registrar, dates, nameservers...') and enumerates the categories of data returned. The scope is unambiguous and clearly distinct from the SERP/report siblings, none of which handle domain registration.

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 gives actionable routing guidance: fresh vs cached lookups and their cost, and explicitly 'Do not call get_balance again when the response already includes balance.' It stops short of naming alternative siblings or explicit when-not-to-use conditions, so it is strong context but not a full 5.

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