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

Beyond the annotations (readOnly, idempotent, non-destructive), the description discloses commercial and operational traits the annotations cannot: 0.02 USDC per call, p95 latency of 4000 ms, and the limitation that registrant personal data is redacted by registries. Those are exactly the behavioral facts an agent needs for cost/retry planning.

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, each load-bearing: one for the payload, one for use/don't-use routing, one for price and latency. The payload enumeration is front-loaded and no sentence is redundant.

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?

An output schema exists, so return-value explanation is not strictly required, yet the description still summarizes the payload sections. Combined with the cost, latency, redaction caveat, and routing guidance, an agent has everything needed to select and invoke this tool correctly.

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% with only two parameters, both fully documented in the schema (including the 'true when omitted' default for certificates). The description mentions certificate transparency output, which loosely motivates the certificates flag, but adds no syntax or format detail beyond the schema, so the baseline of 3 applies.

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 opens with a precise verb-and-resource statement ('Returns JSON with a domain's registration...') and enumerates the exact payload sections: RDAP registrar/dates/status/DNSSEC, DNS records, SPF/DMARC, and TLS certificates. An agent knows exactly what this tool produces without opening the schema, and the 'Do not use' clause keeps it distinct from port/vuln scanners.

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 an explicit positive trigger set ('whois or domain lookup, dns records, email security checks or certificate transparency data for osint or due diligence') and an explicit negative set ('historical whois, registrant personal data, or a port and vulnerability scan'). Both when-to-use and when-not-to-use are spelled out, leaving little to inference.

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