asn_lookup

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

Annotations already mark the tool as read-only and idempotent. The description adds value by explaining the default limit of 50 prefixes per family and that ipv4_count and ipv6_count are 'honest pre-truncation totals'. This provides behavioral context beyond the annotations.

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 concise, front-loading the core purpose, then providing usage guidance and parameter details without redundancy. Every sentence adds value.

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?

Given the tool's simplicity and the presence of an output schema, the description fully covers the necessary context: what the tool does, how to use it, parameter nuances, and expected output fields. It is complete for an agent to select and invoke correctly.

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 100%, but the description enriches both parameters: target includes example formats, and include_full_prefixes includes a concrete example of Cloudflare's prefixes and explains its utility. This goes beyond the schema's brief descriptions.

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 'Look up Autonomous System Number (ASN) for a domain or IP' and lists the return fields, making the tool's purpose immediately evident. It distinguishes from siblings like ip_lookup and whois_lookup by focusing on ASN and network operator identification.

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 provides a clear use case ('Identify network operator and IP range ownership') and contextual advice on when to set include_full_prefixes ('network mapping or BGP route audits'). It also mentions rate limits, guiding appropriate usage. However, it does not explicitly contrast with alternative tools.

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