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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds material context beyond that: it names the data sources (RDAP, RIPEstat), the 400 refusal behavior for non-public ranges, and the x402 payment model including that failed calls are free — valuable for an agent deciding whether to call.

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 with zero padding: what it returns, the failure condition, and the cost model are each front-loaded and earn their place. Nothing is repeated from structured fields.

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?

An output schema exists, so return values needn't be explained; the description still covers the inputs' constraint (public only), the error path (400), the data provenance, and the billing model. An agent has everything needed to decide and call correctly.

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 'ip' parameter is already documented as IPv4 or IPv6. The description adds nothing about format, edge cases, or input handling beyond the schema, 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?

Opens with a specific verb+resource ('Who owns an IP address') and enumerates exactly what is returned: network name, CIDR, owner, abuse contact, ASN, holder, and reverse DNS. An agent can immediately distinguish this from siblings like dns, domain, or evm_address.

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?

Clearly states the operative constraint: private, reserved, and documentation addresses are refused with 400, and only public registry data is used. That tells the agent when the tool will fail, but it does not explicitly name an alternative sibling for those cases, keeping it short of a 5.

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