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 valuable behavioral context: it explains the FCrDNS verification logic, the three possible verdicts, and the caveat that a PTR alone proves nothing. It also discloses that private/loopback/CGNAT ranges are refused. 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 dense but well-organized: it front-loads the trigger condition, then explains the verification logic, verdicts, and caveats. Every sentence earns its place, though it is slightly long. The structure is logical and scannable.

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 single-parameter read-only tool with a rich output schema, the description is complete. It covers when to use it, what it does, what the verdicts mean, the key caveat about PTRs, and the fix location. 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 coverage is 100%, so the schema already documents the 'ip' parameter well. The description adds meaning by explaining what the IP is used for (the sending IP to check), the requirement that it be public, and the refusal of private/loopback/CGNAT ranges. This complements the schema rather than repeating it.

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 ('check') and resource ('one sending IP's forward-confirmed reverse DNS'), and explicitly names the domain (reverse DNS, PTR records, FCrDNS). It distinguishes itself from siblings by focusing on a single IP's FCrDNS check, which is a unique operation among the listed tools.

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 explicitly says when to use it ('when the user asks about reverse DNS, PTR records, or FCrDNS for a mail server IP') and provides clear exclusions: it checks one IP, not multiple; it refuses private/loopback/CGNAT ranges. It also tells the agent what not to do ('never report a bare PTR as verified') and where the fix belongs, which is strong usage guidance.

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