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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds meaningful context beyond that: data sources (registry WHOIS/RDAP and DNS), the specific signals returned, a regional focus on African banks, tax authorities and mobile money, and a concrete pricing model ($0.005 USDC per call via x402 on Base mainnet). It does not cover failure modes such as an unregistered domain or rate limits.

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?

The capability and data sources are front-loaded before use cases and pricing, and every sentence contributes information. The opening sentence is dense with enumerations but not padded, so the length is justified by the breadth of the lookup.

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?

For a multi-source lookup tool with no output schema, the description adequately enumerates what comes back—registry data, DNS, email security and risk flags—plus the pricing model. The main missing piece is how this tool relates to the overlapping domain- and email-security siblings.

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 single parameter's schema already gives examples ('example.com' or a full URL with path). The description adds no further parameter-level meaning, so the baseline of 3 for high-coverage schemas is appropriate.

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 ('WHOIS / RDAP domain lookup') and enumerates the returned data: registrar, dates, age, status, nameservers, DNSSEC, DNS records, email security grade, and risk flags. It does not differentiate from closely related siblings such as za_official_domain_check or za_email_security, leaving the agent to infer which lookup to use.

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 names three contexts ('phishing triage, vendor due diligence and research'), which gives implied usage guidance. However, it offers no when-not-to-use conditions and never references the overlapping sibling tools, so selection among alternatives is left to inference.

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