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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint, so the safety and idempotency profile is fully covered. The description adds value beyond them by stating what is returned (the resolved hostname). It does not mention the common failure case where no PTR record exists, which leaves a small gap.

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 short sentences, with the usage trigger front-loaded and the return value following. No filler, 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 one-parameter read-only lookup with no output schema, the description covers purpose, trigger, and return shape, and annotations cover the safety profile. Only the no-record/failed-resolution behavior is unaddressed, a minor omission for this tool type.

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% and the single parameter is fully documented with example IPs in the schema. The description only restates that the input is an IP address, adding no format or edge-case detail (IPv4 vs IPv6, literal vs hostname). Baseline 3 is appropriate when the schema does the work.

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?

States a specific verb and resource: reverse DNS (PTR) lookup of an IP address, and clarifies the output is the hostname the IP resolves to. This cleanly distinguishes it from siblings like dns_lookup, cname_lookup, and mx_lookup without needing to name them.

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 an explicit trigger ('when the user wants the reverse DNS of an IP address') plus a concrete scenario ('check a sending server's reverse DNS'), which strongly implies usage context. It stops short of naming when to prefer a sibling (e.g., dns_lookup for forward resolution) or any exclusions.

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