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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful context the annotations lack: a cost of 2 credits per call. It says nothing about behavior when no PTR record exists, which is the main failure mode for reverse DNS.

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 purpose is front-loaded and the cost note is well placed at the end, but the opening duplicates the title verbatim ('Fully Qualified Domain: Fully Qualified Domain resolves...'), wasting the most valuable position. The enumeration of return fields is largely redundant given an output schema exists.

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 full schema coverage and an output schema, the definition supplies enough to invoke it correctly, and the credit cost is a welcome addition. The remaining omission is a note on no-PTR-record results, which matters for agent planning.

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% with a single required parameter that is documented and even given an IP example, so the schema carries the load. The description's phrase 'the IP address' restates the schema without adding format or validation detail, making baseline 3 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 uses a specific verb and resource ('resolves an IP address to its fully qualified domain name using reverse DNS PTR records') and names the mechanism, so the operation is unambiguous. It does not, however, distinguish itself from the sibling ReverseDNSLookup, which appears to do the same thing, leaving the agent to guess between 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?

There is no explicit when-to-use or when-not-to-use guidance, and no alternative is named. The closest sibling, ReverseDNSLookup, is never referenced, so the agent receives no routing signal for choosing between two apparently overlapping tools.

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