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

Beyond the annotations (readOnlyHint, openWorldHint, destructiveHint), the description adds crucial behavioral detail: prefixCount is a sampled /24-size proxy, not a count of announced routes, and no API key is needed. These disclosures prevent misinterpretation and misuse without contradicting any annotation.

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?

Three sentences with no filler: the action and result shape come first, the critical proxy caveat is second, and a concrete example closes. Every sentence adds useful information, and the structure is scannable.

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 no output schema, the description fully covers what an agent needs: input format, returned fields, semantics of a tricky field, auth requirements, and an example result. Nothing essential for correct invocation is missing.

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 the schema already documents the asn parameter and its accepted string/integer forms. The description adds a concrete example ('AS15169') and explains how the value maps to the result, but this is marginal enrichment beyond the schema's own examples.

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 states a specific verb ('Look up'), the resource ('autonomous system'), and the lookup key ('by number'), then enumerates the returned fields (name, domain, country, prefixCount). The example makes the intent unambiguous and distinguishes this from the sibling asn_search by emphasizing numeric lookups.

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 makes clear this is for looking up an AS by its number, which implies it is the right tool when a numeric ASN is known. It does not explicitly name alternatives or when-not-to-use conditions, but the 'by number' framing and sibling name asn_search provide sufficient context for selection.

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