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

Beyond the annotations, the description explains that each call is charged, repeats are not free, failed calls are free, and pricing is $0.02 via x402 USDC or a card key with the first 25 free. It also reinforces the read-only nature by saying it reads or computes only and changes nothing, and it frames the verdict as signals rather than a guarantee.

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 front-loads the main value proposition and then adds flags, use cases, limitations, raw-record routing, an example, pricing, and read-only behavior. It is dense but mostly earns its length; the example slightly duplicates the schema and the billing details are detailed, preventing a 5.

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 still explains what the verdict contains: high/medium/low trust, named flags for registration age, expiry, SPF, DMARC, nameservers, web host, non-resolution, plus key facts like registrar, age, nameservers, and DNSSEC. It also covers billing and the signals-only limitation, which is sufficient for a one-parameter lookup tool.

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?

The schema already has 100% description coverage for the single 'name' parameter, including the same example domain. The description adds the example usage 'name=cloudflare.com' but no meaningful syntax or format detail beyond what the schema provides, so the baseline of 3 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: it returns a trust verdict for a domain in one call, with high/medium/low trust, named flags, and key facts. It also distinguishes this from the sibling raw DNS operation by saying 'Raw DNS records: domain,' so an agent can tell which tool gives a verdict versus raw records.

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 clear usage contexts: lead qualification, phishing checks, vendor checks, and before sending mail to or trusting a domain. It also names the raw DNS alternative implicitly via 'Raw DNS records: domain' and warns that results are signals, not a guarantee. It lacks an explicit when-not-to-use statement against other verification siblings, 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.