Reverse DNS (PTR)

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context: it returns an error for invalid IPs or missing PTR records, and it documents the return shape ({ ip, hostnames: string[] }). This goes beyond the annotations without contradicting them.

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 compact and well-structured: a one-sentence purpose, a short Args list, a Returns line, an example, and an Errors line. Every sentence earns its place, and the most important information (what it does) is front-loaded.

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?

The tool is simple (2 params, 1 required, no nested objects) and has an output schema. The description covers purpose, parameters, return shape, example usage, and error behavior. Nothing an agent needs to call it correctly 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 both parameters. The description adds a brief mention of the ip parameter in the Args section and the default for response_format, but it does not add significant new meaning beyond the schema. Baseline 3 is appropriate.

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 ('Resolve'), a specific resource ('PTR records for an IP address'), and clarifies the output ('hostname(s) the IP maps back to'). It distinguishes itself from sibling tools like dns_lookup and mx_lookup by focusing on reverse DNS. The example query further anchors the purpose.

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 gives a clear example of when to use it ('What hostname does 8.8.8.8 reverse to?') and implies it is for reverse lookups, which differentiates it from forward DNS tools. It does not explicitly name alternatives or state when not to use it, but the context signals and sibling list make the use case clear.

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