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

Annotations already establish read-only, idempotent, open-world, non-destructive behavior, and the description adds important operational context: what data is checked, risk levels and flags, accepted inputs, x402 cost, API-key credits, and the first-5-free daily quota. This materially helps an agent understand cost and prerequisites before calling.

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 description is dense but front-loaded: it starts with the use case, then lists the evidence returned, then covers accepted inputs and payment. Every sentence contributes either routing, output expectations, or payment semantics.

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 no-output-schema tool with meaningful complexity, the description lists the key returned data points and risk flags well enough to set expectations. It does not describe the exact response shape, but combined with the rich annotations and complete schema, it is nearly complete.

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 coverage is 100%, so the parameters are already well documented. The description still adds useful meaning by clarifying that the input may be a domain, URL or email, and by explaining when the optional API key matters versus the free-quota or x402 payment paths.

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: judging whether a website or email domain is trustworthy. It enumerates concrete checks such as RDAP registration age, expiry, registrar, nameservers, MX/SPF/DMARC, disposable domains and risk scoring, making it clearly distinct from sibling tools like company dossiers or email verification.

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 a clear usage context: use when you need to judge domain trustworthiness. It does not explicitly name alternatives or when-not-to-use cases, so it falls short of full routing guidance, but the intended context is clear.

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