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

Annotations only say read-only/idempotent/open-world; the description adds the critical interpretive constraint that originHidden=true means the real host is unknown and the CDN must not be reported as the host. It also discloses no-login availability and describes the result shape (confidence, evidence, host.kind enum). This is disclosure beyond what structured fields provide.

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?

Purpose and scope are front-loaded in the first clause, followed by return shape, then the caveat, then usage. The inline enumeration of return fields and the host.kind values is dense but useful for a schemaless return; only minor trimming would help.

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?

There is no output schema, so the description carries the return contract itself — it names every top-level field and the host.kind vocabulary, plus the originHidden interpretation rule. An agent can both call this correctly and report its result honestly without further context.

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?

Only one parameter and schema coverage is 100%, so the schema already fully documents 'domain' including an example. The description adds nothing about domain format, subdomain handling, or normalization rules, 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 specific verb and resource ('Find out WHO HOSTS a website') and enumerates exactly what is resolved: hosting company, CDN, DNS provider, email provider. It explicitly distinguishes itself from the similarly-named detect_technology sibling, which removes the main ambiguity an agent would face.

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 concrete triggering questions ('who hosts a site', 'who a competitor hosts with', 'where a site they inherited is running') and an explicit alternative with its condition ('For the CMS/stack running on top, use detect_technology instead'). This is the when-to-use / when-to-use-something-else pattern at full strength.

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