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

Annotations already declare readOnly, openWorld, idempotent and non-destructive, so the safety profile is covered. The description adds real value by revealing that a single call aggregates IPs, ASN/org, nameservers and CDN detection, but it says nothing about latency, external calls made, or failure behaviour when a domain has no A records.

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?

A single sentence, front-loaded with the purpose and then the enumerated outputs in a natural scan order. No filler, no repetition of the title.

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 one-parameter read-only lookup with full annotation coverage, the description covers what an agent needs: what it queries and what comes back. No output schema exists, and the enumeration of returned fields largely compensates, though edge-case behaviour (no CDN, no nameservers) is unstated.

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?

There is one parameter and schema coverage is 100%, with the schema itself explaining that URLs and email addresses are reduced to their domain. The description adds no further parameter meaning, so the baseline 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?

The description opens with a specific verb-plus-resource ("Finds out who hosts a website") and then enumerates exactly what is returned: IP addresses, network/organisation, nameservers and CDN. An agent can distinguish this aggregate hosting view from narrower siblings like dns_lookup or ip_lookup, though no sibling is named explicitly.

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?

Usage is only implied: an agent can infer this is the one-shot 'who hosts this site' tool versus per-record lookups, but the description never says when to prefer it over whois_lookup, dns_lookup or ip_lookup, nor does it state any prerequisites or exclusions.

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