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

Goes well beyond the annotations: it explains why readOnlyHint=false (each call is charged despite being read-only), discloses pricing, the x402 USDC / card-key credit paths, 25 free calls, free failed calls, and explicitly bounds reliability with 'Signals only, not a guarantee.' This is exactly the behavioral context an agent needs.

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?

Front-loads the purpose and output shape before pricing and caveats, and every sentence carries information. It is dense but slightly overlong, stacking pricing and billing paths that could be trimmed.

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 compensates by describing the return shape (verdict tiers, named flags, key facts like registrar, age, nameservers, DNSSEC). Combined with pricing and the reliability caveat, an agent has everything needed to call and interpret it.

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 is already documented in the schema, so the schema does the heavy lifting. The description only adds a redundant example (name=cloudflare.com), so baseline 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?

States a concrete verb+resource and enumerates the exact output: a high/medium/low trust verdict with named flags for new registrations, expiry, SPF/DMARC issues, nameserver count, and non-resolving domains. It is clearly distinguishable from siblings like 'domain', 'company', and 'check_counterparty' which do not provide a consolidated trust verdict.

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?

Gives explicit when-to-use contexts: lead qualification, phishing and vendor checks, and pre-mail/pre-trust decisions. No named alternative or explicit when-not condition, and it does not distinguish itself from the sibling 'domain' tool, so it stops short of a 5.

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