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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds the non-obvious cost signal "Spends 1 request of your ipapi.is quota," which matters for a metered API. It does not disclose behavior for invalid or unannounced ASNs (empty result vs. error), which is the main remaining gap.

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, front-loaded with the action and returned fields, followed by the quota cost. No filler, no repetition of the name or title.

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 enumerates the returned fields (organization, registry, type, country, announced routes) and discloses quota cost, which is enough to call the tool correctly. Only error/empty-result behavior for a nonexistent ASN is left unspecified.

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 parameter documents the AS prefix format with an example, so the schema carries the semantic load. The description only restates the resource as "AS number" and adds no format or normalization 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 ("Look up one autonomous system (AS number)") and enumerates the returned attributes: organization, registry, type, country, announced routes. The word "one" plus the ASN focus clearly separates it from the sibling tools ipapi_bulk_lookup and ipapi_lookup_ip without needing to name them.

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?

Usage is only implied: an agent can infer this is the tool for a single-ASN lookup, and the quota sentence hints it is a paid call worth conserving. There is no explicit when-to-use guidance, no statement of when to prefer ipapi_bulk_lookup (multiple ASNs) or ipapi_lookup_ip, and no mention of error conditions for an unknown ASN.

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