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

No annotations are supplied, so the description carries the full burden, and it discloses almost nothing: it does not state that the operation is read-only (implied but unstated), whether results are capped or paginated, how many domains are typically returned, or any rate limits. "Runs the same code the tool page runs" is a faint fidelity signal but not behavioral context an agent can act on.

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 short fragments, front-loaded with the resource definition, with no wasted prose. It is terse to the point of being cryptic, but nothing is redundant or buried.

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 tool with no output schema and no annotations, the description should say what comes back (a list of hostnames? a count? empty-result behavior?) and any limits. None of that is present, so an agent cannot anticipate the response shape of a fundamentally list-returning lookup.

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% and the single parameter is already documented as "IPv4 or IPv6 address." The description's "Scope: ip" adds no format, normalization, or CIDR guidance beyond that, so the 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?

"Domains sharing an address" does identify the resource (reverse-IP hostname lookup), but as a noun fragment with no verb and no explicit mention of "IP" as the lookup key it reads more like a page subtitle than a tool statement. It is distinguishable from check_ip and check_dns only by inference; no sibling is named.

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?

There is no when-to-use guidance at all: nothing says when to pick this over check_ip, check_dns, check_asn, or check_whois, which all operate on adjacent data. "Scope: ip" only hints at the input domain, not the selection criteria.

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