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

With no annotations, the description carries the full burden and does reasonably well: it discloses that the operation is a read of public signals only, that it requires no account and is free (no auth), and it explicitly bounds the result ('says nothing about who runs the domain'). It omits rate limits, caching, and failure behavior for unreachable domains, which keeps it short of a 5.

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?

Three tight sentences, front-loaded with the action and signal list, then the return shape, then the scope caveat. No filler, and each sentence carries distinct decision-relevant information.

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?

No output schema exists, yet the description fully specifies the return (score out of 100, grade, per-failure fix) and the cost/auth model. For a single-parameter, no-annotation tool this covers everything an agent needs to invoke 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 'domain' parameter already has an example in the schema, so the baseline is 3. The description adds no format or edge-case detail (IDN, subdomains, scheme handling) beyond what the schema provides.

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?

Specific verb (scans) plus resource (a domain's security passport) and an enumerated scope of thirteen named public signals. The reader knows exactly what is checked and what is returned (score out of 100, grade, failing checks with fixes), and it is clearly distinguishable from network/registration siblings.

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?

Implied usage context is present ('Free, no account'), which tells an agent this is a frictionless read-only diagnostic, but there is no explicit when-to-use/when-not guidance and no routing to or away from any sibling tool. Adequate but with a clear gap.

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