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

With no annotations provided, the description carries the full burden and does so well: it declares the data source (IANA bootstrap to RDAP), auth requirements ('No API key, no account'), the pricing model ($0.005/call via x402 USDC), and the important edge case that a TLD lacking an RDAP server is reported as such rather than as unregistered. That last disclosure prevents a real misinterpretation of the result.

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?

Opens with the usage trigger, then the data source, then the returned fields, then cost/auth — a sensible front-loaded order with no filler. Every clause contributes either routing information or behavioral context.

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?

The tool is simple (one required parameter, no output schema), and the description compensates by enumerating the returned fields (creation/expiry/last-change dates, age, days to expiry, registrar, EPP status, nameservers, DNSSEC, abuse contact). An agent can decide and call correctly without further information.

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% and the schema already explains that a URL or email is reduced to its host. The body text adds nothing about the domain argument, so this sits at the baseline for a well-documented single parameter.

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 read from the registry's own RDAP service') and explicitly contrasts with port-43 whois scraping, which pins down what kind of data this returns. It doesn't distinguish itself from adjacent siblings like red_domain_check or red_cert, so an agent must infer that boundary itself.

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?

Names two concrete trigger conditions: judging how established a domain is, and checking when it expires. There are no explicit exclusions or named alternatives, but the stated triggers are clear enough to route most calls correctly.

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