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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds real value by enumerating the lookup result facets and clarifying the negative boundary (no reachability testing), which no annotation expresses. It stops short of noting rate limits or lookup latency, keeping it below a 5.

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 short sentences, front-loaded with the verb and resource, then use cases, then the exclusion. Every clause carries information; nothing is padding.

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?

An output schema exists, so return-value documentation is not required, yet the description still sketches the result fields usefully. Combined with the explicit sibling routing and the confirmed read-only profile, an agent has everything needed to select and invoke it 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 description coverage is 100%, so the format examples for 'input' are already documented in the schema. The description adds only the dual nature (IP or ASN) at a high level, which the schema also conveys. Baseline 3 is appropriate given the schema does the heavy lifting.

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?

Specific verb 'Look up' with dual resource 'IP address or ASN', and it enumerates exactly what comes back (owner org, announced prefix, PTR, RPKI validity, geolocation). The closing clause distinguishes it from check_port, so an agent can separate it from siblings without opening any schema.

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?

Gives concrete triggering situations ('identify who is behind an address seen in logs or headers, or to check PTR / RPKI for a mail or BGP issue') and an explicit exclusion with the alternative named: 'Does not test reachability (use check_port).' When-to-use, when-not, and the sibling to use instead are all present.

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