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

With no annotations provided, the description carries the full burden of behavioral disclosure. It mentions 'via Team Cymru DNS' but does not disclose any limitations, rate limits, input format requirements, error behavior, or network dependencies. For a tool that performs a network query, this is a significant gap; the agent has no warning about potential failure modes or prerequisites.

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 description is a single, efficient sentence with no filler. It front-loads the core purpose and method, and the claim 'fastest ASN lookup' is concise and useful. Every word earns its place, making it an excellent example of brevity.

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 simple one-parameter tool with an output schema, the description is mostly adequate. However, it omits critical details like the expected input format (IP address type) and any potential caveats (e.g., rate limits, need for internet). Given the abundance of sibling ASN tools, additional context on when this tool is uniquely appropriate would improve completeness. It is minimally viable but not fully comprehensive.

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 coverage is 0% for the single parameter 'q', so the description must compensate. It does so by implying that 'q' is an IP address ('IP → ASN'), adding meaning beyond the bare schema. However, it does not specify the expected format (IPv4/IPv6, CIDR, etc.) or provide any further clarification, leaving room for misinterpretation.

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 clearly states the tool's function: IP to ASN lookup using Team Cymru DNS. It names a specific resource and method, and even adds a distinguishing claim ('fastest ASN lookup'). While it doesn't explicitly differentiate from sibling tools like asnlookup or asn, the purpose is unambiguous enough for an agent to understand the core operation.

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 description offers a hint about when to use this tool ('fastest ASN lookup') but does not explicitly state when to prefer it over alternatives or when not to use it. With many sibling ASN tools present, there is no clear routing guidance beyond the speed claim, leaving the agent to infer usage context.

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