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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely non-structured context: a cost of 1 credit per call and the fact that only open registry data is consulted, which affects expectations about freshness and coverage.

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?

Two short sentences that front-load purpose and then cost/output. The trailing inline JSON shape is dense but informative; nothing is wasted, though the output sketch could have been prose.

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 usefully sketches the return shape (ip, version, is_private, reverse_dns, network fields) and discloses cost. For a single-parameter read tool this is nearly complete; only sibling differentiation is missing.

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 'ip' parameter is fully documented as a public IPv4/IPv6 address, so the baseline is 3. The description reinforces the public-address constraint but adds no syntax or format detail beyond the schema.

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 names a specific resource (reverse DNS name and registry record of a public IP) and states the data source ('open registry data only'), so the agent knows exactly what this returns. It does not, however, contrast itself with the same-domain siblings dns_lookup and rdap_lookup, leaving overlap unexplained.

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?

The only usage constraint given is 'public IP address'; there is no guidance on when to prefer this over dns_lookup or rdap_lookup, which appear to cover adjacent ground. Cost is stated, but no when/when-not framing is offered.

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