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

Goes well past the annotations by disclosing the cost model ($0.01 USDC on Base, x402, charged per *successful* call) and the reliability caveat that output is signals, not a guarantee. It also reconciles the odd readOnlyHint=false by implying a payment side effect, and enumerates the output content in enough detail to substitute for the absent output schema.

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 value proposition ('A trust verdict for any domain in one call') before the flag inventory and pricing. The first sentence is a long comma-stuffed list, but nothing is padding and the sentence order is sensible.

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 fully carries the burden: it names the verdict scale, the specific flags, and the key facts returned, and it discloses cost and the signals-only caveat. An agent has everything needed to call it and interpret results.

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 there is a single, obvious `name` parameter with an inline example, so the schema already does the heavy lifting. The description's 'any domain' adds only marginal meaning over that baseline.

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 deliverable (a high/medium/low trust verdict) plus the concrete flags and facts it returns (new registration, expiry, SPF/DMARC, nameservers, DNSSEC). This clearly separates it in spirit from the generic sibling `domain` lookup, though it never names that sibling to make the distinction explicit.

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 contexts: lead qualification, phishing/vendor checks, and pre-send-mail trust decisions. It also states the boundary 'signals only, not a guarantee.' It does not, however, name an alternative or exclude any scenario, so it stops short of full when/when-not routing.

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