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 genuinely new behavior: each call consumes one unit of the key's monthly quota, and risk_signals plus security flags are gated behind the Pro plan. It says nothing about failure modes such as invalid, private, or reserved addresses, so it goes beyond annotations without fully covering behavior.

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?

The output content is front-loaded, followed by the quota cost and then the sibling routing, which is a sensible order. The opening sentence is dense and overloaded with field names, but no sentence is filler.

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 compensates by listing the returned fields, including plan-gated ones, and it discloses cost per call. It stops short of covering error or edge cases (private or malformed addresses, quota exhaustion), which is a modest gap for a one-parameter 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?

There is one parameter with 100% schema description coverage, including example IPv4 and IPv6 forms, so the schema does the heavy lifting and the baseline of 3 applies. The description reinforces the 'public' restriction, which is useful, but adds no format or validation 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?

States a specific verb and resource ('lookup ... ONE public IPv4 or IPv6 address') and enumerates what comes back: geolocation, ISP/ASN, risk score with risk_reason, plus Pro-only breakdown. The single-address scope plus the explicit pointer to bulk_lookup separates it from the sibling without needing the schema.

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 an explicit selection rule: one address here, two or more goes to bulk_lookup in a single call. It does not address when a different sibling such as check_ip_risk would be the better choice, so guidance is strong but not exhaustive.

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