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

With no annotations, the description carries the full burden and does substantial work: it discloses the data source (RDAP via IANA bootstrap), the auth model (no API key, no account), the cost ($0.005 per call over x402/USDC), and the key edge case (TLDs with no RDAP server say so rather than reporting unregistered). Rate limits and failure modes are not covered, keeping it short of 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?

Four dense sentences, front-loaded with what the tool is and where the data comes from. Every sentence adds information, though the pricing and bootstrap details could be compressed slightly.

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 enumerating the returned fields (creation/expiry/last-change dates, age, days to expiry, registrar, EPP status codes, nameservers, DNSSEC, abuse contact) plus the edge-case return behavior. An agent knows what it will get and what it costs before calling.

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?

Only one parameter and schema description coverage is 100%, so the schema already explains that URLs and emails are reduced to their host. The description adds nothing beyond 'one domain', which is the correct baseline when the schema does the heavy lifting.

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 and resource ('Registration data for one domain') and immediately differentiates the mechanism from port-43 whois scraping. It also implicitly separates itself from the sibling red_domain_check by framing itself as registration data rather than availability.

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 is implied ('one domain', registration data) but the description never states when to pick this over red_domain_check or red_dnsbl, nor any exclusions. The agent can infer the context but must do the routing work itself.

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