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

Annotations already declare readOnlyHint=true, so the description doesn't need to argue safety. It does add genuine context beyond annotations: the quota cost ("spends 1 request of your ipapi.is quota") and the concrete field set returned, which is the main thing an agent needs for a read-only lookup. Missing only error/empty-result behavior for a 5.

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 sentences, no filler, and the resource/scope is front-loaded before the quota caveat. Every clause carries information an agent can act on.

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 enumeration of returned fields (including the individual is_* flags) does the job of describing the response shape, which is the main completeness risk here. What is left thin is the effect of the two optional boolean parameters, though the schema covers them well.

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%, so all three parameters are already documented, making the baseline 3. The description adds no meaning for the optional all_companies or geolocation_sources switches; its field list reflects the default response, not the parameter effects.

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 the specific verb (look up), resource (one IPv4/IPv6 address), the provider (ipapi.is), and enumerates exactly what is returned (company, network, abuse contact, location, and seven flags). The word "one" implicitly contrasts with the bulk sibling, and the ASN sibling is clearly a different resource, so an agent can distinguish them without opening schemas.

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 single-address scope and the quota cost hint at when this is appropriate versus ipapi_bulk_lookup, but the routing is only implied — it never names the alternative or says "for multiple addresses use bulk." No exclusions or prerequisites are stated.

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