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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely useful non-schema behavior: a 4-credit cost and the fact that the returned field set varies by plan tier (registry handle, country code, IP range stats only on paid plans). However, it does not say what happens on a free plan or whether the tool errors or silently omits fields, which is the obvious follow-on question.

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, front-loaded with purpose, followed by the tiering/cost caveat. No filler and no repetition of the 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?

For a single-parameter read-only lookup with an output schema and full annotation coverage, the description covers purpose, cost, and result variability across tiers. The only real gap is lack of input-format guidance and sibling disambiguation.

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 only one parameter and schema description coverage is 100%, including an 'AS15169' example, so the schema carries the full burden. The description adds nothing about accepted formats (with or without the 'AS' prefix, numeric-only input), leaving that entirely to the schema example.

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 uses a specific verb ('resolves') with a specific resource ('any Autonomous System Number') and names what comes back ('registered organization name and numeric identifier'). It is clearly distinguishable from neighbors like IPLookup or WHOISLookup, though it never explicitly names an alternative.

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?

There is no guidance on when to use this versus related siblings such as IPLookup, WHOISLookup, or IPDemographics, and no preconditions or exclusions. The only contextual information is the credit cost and the plan-tier note, which is pricing rather than usage guidance.

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